Cleanup: warning on windows

Nodes: add geometry socket type

We still have to pick a color for this socket.

Ref T81848.

Cleanup: remove dead code

Fix compile error

Haven't tested on windows, hope that works.

Volumes: simplify volumes in modifiers or on load

This changes how the simplify volumes setting works. Before, it only
affeted viewport rendering. This was an issue, because all internal
computations would still have to happen on the high resolution volumes.
With this patch, the simplify setting already affects file loading and
procedural generation of volumes.

Rendering does not have to care about the simplify option anymore,
it just gets the correct simplified version from the depsgraph.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D9176

Fix T81684: node location not handled correctly

Reviewers: ISS

Differential Revision: https://developer.blender.org/D9236

Fix: skip drawing input sockets that do not have a draw method

Contributed by @povmaniaco with minor changes by me.

Differential Revision: https://developer.blender.org/D9263

Volumes: new Volume to Mesh modifier

This modifier is the opposite of the recently added Mesh to Volume modifier.
It converts the "surface" of a volume into a mesh. The "surface" is defined
by a threshold value. All voxels with a density higher than the threshold
are considered to be inside the volume, while all others will be outside.

By default, the resolution of the generated mesh depends on the voxel
size of the volume grid. The resolution can be customized. It should be
noted that a lower resolution might not make this modifier faster. This
is because we have to downsample the openvdb grid, which isn't a cheap
operation.

Converting a mesh to a volume and then back to a mesh is possible,
but it does require two separate mesh objects for now.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D9141

Cleanup: clang tidy

Cleanup: reduce variable scopes