Mostly internal changes, keeping both manipulators
could have worked but there was no point long term.
There are still some glitches to resolve, will work on those next.
Adding alongside the existing one for now,
but it should eventually replace it.
Uses a matrix instead of (position + scale),
written so rotation can be done more easily.
Currently has a primitive handle for rotation, supports corner scaling.
A single manipulator could only assign a single operator to each part.
Now each part can have it's own.
Also modify 2D selection callback, 2D started at 1, 3D at 0.
Now use -1 for unset value, start both at 0.
Some manipulators are used like on-screen buttons,
in this case it doesn't make sense to keep track of their state,
so zero the offset when its unused.
Needed for lamp-target manipulator.
Re-use operator return flags for manipulator modal & invoke,
this means manipulators can allow navigation or other events to be
handled as they run - see T52499
2.8x branch added bContext arg in many places,
pass eval-context instead since its not simple to reason about what
what nested functions do when they can access and change almost anything.
Also use const to prevent unexpected modifications.
This fixes crash loading files with shadows,
since off-screen buffers use a NULL context for rendering.
Was complicating general use case, also support for transforming with matrix_space set.
Add matrix_space support for manipulator_window_project_2d too.
Also internal changes so arrow3d matches grab3d's behavior.
Needed to add WM_MANIPULATOR_DRAW_OFFSET_SCALE flag so
we can optionally apply offset in worldspace or screen scaled values.
Render-border & crop-node 2d-cage manipulators where unreasonably
complicated to implement because there was no good way to define
the sub-region the manipulator was transforming in
(render border within the camera's frame for example).
Add matrix-space variable,
remove scale property from cage2d manipulator, use matrix instead.
Was doing this with property get/set but this made view operations
require refreshing manipulator properties.
Simplify by operating on properties in their own space.
Also disable clamping for now since it assumes pixel-space.
