3D View, Objects menu: Always show Assets sub-menu

Now that object assets are no longer considered experimental, the Assets
submenu can always be shown (regardless of the Extended Asset Browser
experimental feature).

Don't deselect assets in `ED_fileselect_activate_by_id`

`ED_fileselect_activate_by_id()` activates an asset (i.e. marks it as
the active asset in the asset browser). To avoid an "active but not
selected" state, it also selects it.

Before this commit, the function would also deselect all other assets,
but that's considered doing too much. If deselection is required, the
`ED_fileselect_deselect_all()` function can be called.

Manifest Task: T92152

Add Assets menu to 3D View's Object menu

In the 3D Viewport, add an "Assets" submenu to the Objects menu, for the
same operators as available in the outliner: Mark as Asset, Clear Asset,
Clear Asset (Set Fake User).

Since object assets are still considered experimental, the menu is only
shown when the Extended Asset Browser experimental feature is enabled.

3D View context: return "ok" when fetching view3d context dir

`view3d_context()` would return `-1` ("found but not available") when
fetching the context dir. This is incorrect; it should return 1 ("ok").

This is a semantic change in preparation of further cleanup of the code.

Cleanup: 3D View context, use enum values

Use explicit enum values instead of returning 0/1 from `view3d_context()`.

No functional changes.

Cleanup: 3D View context, early returns for clearer flow

Refactor `view3d_context()` to use early `return`s instead of a bundle of
`if`/`else if`/`else`, some of which had `return`s and some not.

No functional changes.

Assets: allow Mark/Clear Asset operators from 3D Viewport

Make it possible to run `ASSET_OT_mark` and `ASSET_OT_clear` operators from
the 3D Viewport. There is no menu entry, just compatibility with pressing
F3 and executing the operators from the operator search.

CMake: expand instructions for accidental 'cmake' run in source dir

Our CMake setup refuses to run from the source directory (i.e. Blender does
not support in-source builds). Instead, it shows instructions on how to
clean up after an accidental `cmake` invocation. These instructions missed
one directory that should also be removed (`CMakeFiles`), so that's been
added to the message now.

No functional changes to Blender or the build.

Asset Browser: apply search filter to tags as well

The search bar in the asset browser now also matches on asset tags.

- Matching is done on entire tags, so searching for "redder" will not
show assets tagged with "red".
- All assets are shown that have at least one matching tag. So searching
for "red green" will show all assets with either "red" or "green" tags
(or both, of course).
- Searching is case-insensitive.
- Only assets from the active catalog are shown; if all assets should be
searched through, users can select the "All" catalog.

Manifest Task: T82679

Cleanup: refactor filelist filter functions

Perform a few cleanups:

- Add documentation to explain what returned bools mean.
- Early returns so that flow is clearer and some checks on `is_filtered`
are no longer necessary.
- Split up `is_filtered_file` and `is_filtered_id_file`, so that they can
reuse common code, and such that the different filter checks they
perform can be separated from each other.

The latter is done not only to reduce code duplication, but also as
preparation to fix the asset browser filtering. For that, it helps when
the "filter by file name" and "filter by file type" parts are separate.

No functional changes.

Reviewed By: mont29

Differential Revision: https://developer.blender.org/D12991