Fix (unreported) Smart UV Project not adding UVMap

Since porting this to C in rB850234c1b10a, Smart UV Project would not
add a UVMap (if none existed already) anymore.

Not having a UVMap already is a reasonable situation though when e.g.
starting off fresh by deleting an existing UVMap or also when applying
certain generative modifiers. This is also inconsistent with all other
unwrap operators (all of them will create a UVMap if none exists
already)

Differential Revision: https://developer.blender.org/D9001

Fix T81057: PoseBone Constraints are displayed in Object Constraints tab

Own mistake in rB9dcae4eb17d7b.

We cannot use ED_object_constraint_active_list in uiTemplateConstraints
since it is dependent on mode (pose vs. object). Now get object
constraints directly when use_bone_constraints is false.

Note: unfortunately a derivate of this bug has made its way into 2.90.1

Maniphest Tasks: T81057

Differential Revision: https://developer.blender.org/D8989

Fix T81081: GPencil preset error

Caused by still having 'texture_opacity' in the preests and the preset
operator (but this was removed in the 2.83 rewrite).

Maniphest Tasks: T81081

Differential Revision: https://developer.blender.org/D8990

Fix T81013: Weight Paint Overlay XRay fails with clipping

When introduced in rB1ca1744c29e2, the Weight Paint Overlay XRay's
corresponding depth pass was not considering clipping planes.

Maniphest Tasks: T81013

Differential Revision: https://developer.blender.org/D8970

Fix T80996: Weight Proximity modifier: crash going to editmode on a
target in certain situations

Regression from rBdeaff945d0b96.

mesh_ensure_looptri_data would overflow.

Crash would only happen if a Data Transfer modifier (transferring
UVs) follows, so exact reason for this is not yet entirely clear. Also
there are edit-mode versions of the following BVH lookup functions so it
could be avoided (since this is a expensive operation), marking as TODO.

Similar fix as
- rB0945a79ed1eafae444d3021a5912cb39801a7209
- rB56d7e39b92997768b3db8ce2dbc262f869994145

Reviewers: mont29, campbellbarton

Maniphest Tasks: T80996

Differential Revision: https://developer.blender.org/D8973

Fix T80464: Crash deleting bone constraints when the armature layer is
not active

Caused by {rB608d9b5aa1f1}

Prior to rB608d9b5aa1f1, the constraint was gotten using **context**
[CTX_data_pointer_get_type(C, "constraint", &RNA_Constraint) -- which is
valid for bones on hidden layers].
After rB608d9b5aa1f1, the constraint is found (or isnt) using
`edit_constraint_property_get` [this is **not** valid for bones on
hidden layers because internally `BKE_pose_channel_active` checks if the
bone is on an active layer].

Some observations:
- Every operator using `edit_constraint_property_get` doesnt work for
bones on inactive layers [delete, moveup, movedown, move to index (drag
n drop nowadays)]
-- moveup, movedown, move to index check if they could find a constraint
beforehand though (dont crash)
-- delete crashes (doesnt check if a constraint could actually be found)
- Every operator using `edit_constraint_property_get` for constraint
data doesnt work for bones on inactive layers [stretchto_reset,
limitdistance_reset, childof_set_inverse, ...]
-- these all check if they could find a constraint beforehand though
(dont crash)

This is because the poll function is using **context** to get the
constraint, the operators themselves use
**edit_constraint_property_get** which leads to inconsistent/unexpected
results.

Possible solutions were:
- [1] let the delete operator just work with the context constraint
again (like prior to rB608d9b5aa1f1) -- allows for deleting constraints
on bones in inactive layers
- [2] check if we could get a constraint -- prevents the crash, but does
**not** allow for deleting constraints on bones in inactive layers
- [3] make the poll `edit_constraint_poll_generic` be as strict as the
operators -- dont use **context** to get the constraint, but something
like **edit_constraint_property_get**
- [4] make the operators be more graceful and let them act on bones on
hidden layers -- let **edit_constraint_property_get** actually use the
same **context**

This patch implements [4], so poll an doperators are now in sync.
- prevents reported crash
- also enables operators for bone constraints on hidden layers
- also enables drag and drop reordering of constraints on hidden layers

This might be a candidate for 2.90.1? (if it is, take care to include
prior "Refactor getting constraints" refactoring commit)

Note: Adding constraints also doesnt work for bones on inactive layers
[that was the case in 2.79 as well -- it is also using
`BKE_pose_channel_active`]

Maniphest Tasks: T80464

Differential Revision: https://developer.blender.org/D8805

Fix for failing constraints test

Caused by own rB6dc7266cf1f4.

When overriding context for constraint operators (such as in constraint
tests), it could happen that context "active_pose_bone" is set, but
"pose_bone" isnt. Now check for both in ED_object_pose_constraint_list.

Refactor getting constraints

This is the refactoring part of D8805 (should be no functional changes).

- exposes pose-related part of former 'get_constraints()' from
interface_templates.c to new ED_object_pose_constraint_list
- rename ED_object_constraint_list_from_context -->
ED_object_constraint_active_list

Also clarify comments on both of these.

ref T80464
ref https://developer.blender.org/D8805

Fix T80900: Crash lasso-selecting in particle editmode in certain
situations

In the situation that the PTCacheEdit is not available (e.g. when
editing unbaked Cloth or Softbody caches - or, as in the report, being
in Cloth or Softbody Editing Type for Hair particles), accesing the
corresponding ParticleSystem or ParticleSystemModifierData would crash.

Now access these later (after PE_start_edit had the chance to return
early on this non-valid situation).

Reviewers: JacquesLucke

Maniphest Tasks: T80900

Differential Revision: https://developer.blender.org/D8941

Fix T80905: GPencil: bones cannot be selected using Ctrl + LMB (with Left Selection Preference)

Was missing a dedicated entry for LMB select, this is to be consistent
with how it is done for meshes.

Maniphest Tasks: T80905

Differential Revision: https://developer.blender.org/D8935