Blender Git Loki

various little fixes and cleanups

fix reading normals

Add Custom Object Space to Constraints

Add Custom Space to the list of space conversions for constraints.

Constraints can use World Space, Local Space, Pose Space, Local with
Parent, and now also Custom Space with a custom object to define the
evaluation space.

The Custom Space option uses the Local Space of an other
object/bone/vertex group. If selected on owner or target it will show a
box for object selection. If an armature is selected, then it will also
show a box for bone selection. If a mesh object is selected it will show
the option for using the local space of a vertex group.

Reviewed By: #animation_rigging, sybren, Severin, angavrilov

Differential Revision: https://developer.blender.org/D7437

Fix linker errors when building without Cycles

Fix linker errors by explicitly linking PugiXML when OpenImageIO is
used.

PugiXML has been separated from OpenImageIO (D8628). This means that any
time OpenImageIO libraries are linked, the PugiXML libraries have to be
linked as well. This was set up correctly for Cycles, but not for imbuf.
Because of this, building without Cycles but with OIIO would produce
linker errors.

Fix accendental copy/paste errors after last commit

Bmesh: Improve documentation of op parameters

These comments are used to generate Py API docs.
Most of the comments are just copies of the mesh operator counterparts.

More improvements can be made here in the future.

Thanks to Jon Denning on twitter:

https://twitter.com/gfxcoder/status/1334178566993555459

Merge branch 'temp-review-asset-browser-ui' into asset-browser

Merge branch 'master' into asset-browser

Merge branch 'temp-review-asset-filelists' into temp-review-asset-browser-ui

Merge branch 'temp-review-asset-repositories' into temp-review-asset-filelists

Merge branch 'temp-review-asset-drag-drop' into temp-review-asset-custom-repositories

Merge branch 'temp-review-asset-previews' into temp-review-asset-drag-drop

Merge branch 'temp-review-asset-create-ui' into temp-review-asset-previews

Merge branch 'temp-review-asset-metadata' into asset-metadata-creation

Merge branch 'master' into tmp-review-asset-metadata

Sync with review branches

Some minor changes (mostly cleanups) done while splitting up the branch for review.

Cleanup: view-port --> 2D/3D Viewport

Asset Browser UI

This introduces the UI part of the Asset Browser.

Additions:
* Asset Browser as sub-editor of the File Browser.
* Asset repository dropdown, showing "Current File" and all custom repositories.
* Display popover, filter popover and search box (partially dummies, see T82680).
* Navigation region showing asset categories.
* Asset metadata editing UI in the sidebar (preview, description, tags).
* Make asset files draggable (with preview image).
* If a repository with invalid path is selected, draw a message in the main region to help the user understand what's wrong.
* Operators to add and remove asset tags.
* "Only Assets" option for Link/Append.

Differential Revision: https://developer.blender.org/D9725

Asset Browser: Internal File Browser changes & Python API additions

The Asset Browser will be a sub-editor of the File Browser. This prepares the File Browser code for that.

**File-Lists**
* Support loading assets with metadata read from external files into the file-list.
* New main based file-list type, for the "Current File" asset repository.
* Refresh file-list when switching between browse modes or asset repositories.
* Support empty file-lists (repository with no assets).
* Store file previews as icons, so scripts can reference them via icon-id. See D9719.

**Space Data**
* Introduce "browse mode" to differeniate between file and asset browsing.
* Add `FileAssetSelectParams` to `SpaceFile`, with `FileSelectParams` as base. Makes sure data is separated between asset and file browsing when switching between them. The active params can be obtained through `ED_fileselect_get_active_params()`.
* `FileAssetSelectParams` stores the currently visible repository ID.
* Introduce file history abstraction so file and asset browsing can keep a separate history (previous and next directories).

**General**
* Option to only show asset data-blocks while file browsing (not exposed here).
* Add "active_file" context member, so scripts can get and display info about the active file.
* Add "active_id" context member, so `ED_OT_lib_id_load_custom_preview` can set a custom ID preview. (Only for "Current File" repository)
* Expose some of `FileDirEntry` in RNA as (non-editable). That way scripts can obtain name, preview icon and asset-data.

Differential Revision: https://developer.blender.org/D9724

Asset Browser: Support custom asset repository paths through Preferences

Idea is simple: In {nav Preferences > File Paths}, you can create custom repositories, give them a name and select a path.
Currently, this has to be a path to a .blend, only .blend files are supported as repositories right now. But directories should be supported as well, see {T82682}.

Differential Revision: https://developer.blender.org/D9722