Use a map to speed up search for UI block names.
Time to redraw the node editor was decreased from
around 75-120ms to 40-70ms in a tree with many
Geometry Nodes.
Differential Revision: https://developer.blender.org/D13225
This allows the use of better/more readable data structures,
and will also make some refactors to the search button easier.
The build completed on the buildbot for all platforms.
