Since brush assets were merged, the brush asset selector and some other
brush UIs wouldn't show up for the primitive tools.
Turns out that these primitive tools were never tagged as using brushes
by setting the `data_block` member (or setting the `'USES_BRUSHES'`
option since blender/blender!125911). The UI was just hardcoded to
display things like the brush selector for primitive tools. So as far as
the tool system knew, these tools did not use brushes.
Tagging the tools properly exposed some issues:
- Tool settings displayed twice. Removed the redundant UI definitions.
- Custom tool cursor would be overridden by brush cursor. Fixed by not
activating brush cursors if tools have their own cursor defined.
- Interactions like mouse presses would not be registered by the tool,
events were blocked by the grease pencil stroke keymap. Fixed by
disabling the grease pencil stroke keymap while the primitive tools
are active.
