GH-595 Improve initial rendering of variable type selection

[Naros]

Fixes #595

• All search items (excluding root item) are collapsed when the search box is empty.
• There is no initial search text in the search box.
• All global enums and bitfields have been relocated under new Types/Global Enum and Types/Global Bitfield categories.
• Fixes clearing search box to reset favorite button press state.

[Naros]

Applied to main (=2.1) and branch 2.0