Blender Git Loki

UI: Dim color of shortcut label in menus and toolbar

The shortcut labels now use the "Item" theme color. Its contrast for hovered
items is a bit low, but not too bad.

Note that this also changes the color of the little toolbar triangle to be grey
(the same color we use for the keymap label). IMHO that looks better though.
This doesn't update any themes other than the default one.

Part of T54711.