This adds attribute search to the geometry nodes modifier
for the input and output attributes. The "New" search item
is only shown for the output attributes.
Some of the attribute search code is extracted to a new file
in the interface code, to avoid some code duplication.
The UI code required two fixes so that the search would work
for dynamic length strings (IDProperties do not have a fixed size).
Since this does changes to the UI layout of the modifier, I also
addressed T91485 here.
Differential Revisiion: https://developer.blender.org/D12788
This follows three main targets:
* Make creation of new tree UIs easy.
* Groundwork to generalize tree UIs (so e.g. Outliner, animation
channels, asset catalogs and spreadsheet data-sets don't have to
re-implement basic tree UI code) or even other data-view UIs.
* Better separate data and UI state. E.g. with this, tree-item selection
or the open/collapsed state can be stored on the UI level, rather than
in data. (Asset Catalogs need this, storing UI state info in them is
not an option.)
In addition, the design should be well testable and could even be
exposed to Python.
Note that things will likely change in master still. E.g. the actually
resulting UI isn't very nice visually yet.
The design is documented here:
https://wiki.blender.org/wiki/Source/Interface/Views
Differential Revision: https://developer.blender.org/D12573
