This commit is a refactor of the fill tool to solve several problems we had since the first version of the tool.
Changes:
* The filling speed has been improved for each step of the process with the optimization of each algorithm/function.
* New `AutoFit` option to fill areas outside of the viewport. When enable, the total size of the frame is calculated to fit the filling area.
* New support multiframe filling. Now it is possible to fill multiple similar frames in one go.
* New `Stroke Extension` option to create temporary closing strokes. These strokes can be displayed and adjusted dynamically using wheel mouse or PageUp/Down keys.
* Parameter `Resolution` now is named `Precision` and has been moved to topbar.
* `Resolution` now has decimals and can be lower than 1 to allow quick filling in storyboarding workflows. Maximum value has been set as 5.
* Parameter `Simplify` has been moved to Advanced panel.
* Improved fill outline detection. In some cases, the outline penetrated the area to be filled with unexpected results.
* Fixes some corner case bugs with infinite loops.
As a result of this refactor, also these new functionalities has been added.
* New support for multiframe in `Draw` mode. Any drawing in active frame is duplicated to all selected frame.
* New multiframe display mode. Keyframes before or after of the active frame are displayed using onion colors. This can be disable using Onion overlay options.
This tool implements smearing for multires displacement over the limit
surface, similar to how smearing for colors and topology slide works.
When used the displacement values of the vertices "slide" over the
topology, creating the effect of smearing the surface detail.
As the brush just modifies displacement values instead of coordinates,
the total displacement of the affected area doesn't change. This means
that this smearing effect can be used multiple times over the same area
without generating any artifacts in the topology.
When the brush is used with the pinch or expand smear modes,
displacement differences are pushed into the same area, creating hard
surface effects without pinching the topology.
As any other brush that relies on the limit surface (like displacement
erasers), this will work better after using apply base.
Reviewed By: sergey, JulienKaspar, dbystedt
Differential Revision: https://developer.blender.org/D9659
