Geometry Nodes: fix losing data when attribute has incorrect type

Differential Revision: https://developer.blender.org/D10165

Geometry Nodes: new Attribute Sample Texture node

This node allows sampling a texture for every vertex based on some
mapping attribute. Typical attribute names are the name of a uv map
(e.g. "UVMap") and "position". However, every attribute that can be
converted to a vector implicitly is supported.

It should be noted that as of right now, uv map attributes can only be
accessed after a Point Distribute node.

Ref T82584.

Differential Revision: https://developer.blender.org/D10121

Geometry Nodes: initial support for volumes

For the most part, this just adds boilerplate code for volume support in geometry nodes:
* Add `VolumeComponent` next to `MeshComponent`, etc.
* Support `VolumeComponent` in depsgraph object iterator.

Furthermore, I added initial volume support in a few nodes:
* The Object Info node outputs an object instance when the input is a volume object
(that will be the same for mesh objects soonish, to avoid copies).
* Support transforming a `VolumeComponent` in the Transform node.
* Support the `VolumeComponent` in Join Geometry nodes, but only when just one of the
inputs has a volume component for now.

Right now, there is no way to create a `VolumeComponent`, because the Object Info node
outputs an object instance. The `VolumeComponent` will be necessary for upcoming nodes,
which will generate volumes on the fly.

Viewport selection does not work correctly with `VolumeComponent`s currently. I don't
know why that is. That can be figured out a bit later, once we can actually create
new volumes in geometry nodes.

Ref T84604.

Differential Revision: https://developer.blender.org/D10147

Volumes: fix calling BKE_volume_load from multiple threads

`BKE_volume_is_loaded` uses `grids.filepath` to determine if the
grids are already loaded. The issue was that `grids.filepath` was
set before the grids were loaded, resulting in incorrect early
returns for other threads.

Differential Revision: https://developer.blender.org/D10150

Geometry Nodes: pass depsgraph to nodes during execution

The depsgraph will have to be accessed in an upcoming patch.

initial volume transformation support

initial working volume

integrate with depsgraph iterator

initial volume component

Merge branch 'blender-v2.92-release'