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
