...are not submitted to respective Tool Options sliders

Treat brush angle and aspect ratio like all other paint options values
that can be linked to brush defaults and take their default values
from the brush. They were special casing their defaults to constants,
and GimpBrushGenerated was adding the passed dynamic radius and aspect
values to its own. This was totally incomprehensible.

Now GimpBrushGenerated's transform_size() and transform_mask()
implementations just translate between these APIs value ranges and the
brush's own value range and only use the passed values (not the
brush's native values), which makes the editor <-> tool options
interaction and the painted brush shape predictable.

Also connect the active brush's property notifications to the paint
options properties, so the paint options follow a brush edit live if
the respective "linked" toggles are checked.

And some cleanup.