Editmode should display the original (non-evaluated) points unless there
is something like an "On Cage" option of a modifier [which none of the
curves modifiers have].
This was not the case since the introduction in rBe15320568a29.
So we now draw the editpoints from the original curves. This also means
that original and evaluated curves might not have the same number of
points, so we have to get independent of proc_point_buf since that
would possibly create vertexbuffers of different sizes (compared to the
original curves) which is not allowed for a single batch.
- remove the "pos" alias from the vertex buffer format of proc_point_buf
- instead, create a new "edit_points_pos" vertex buffer
- fill that with the original (un-evaluated) curves positions
- dont request proc_point_buf anymore
- rename the editpoints flags buffer to be more consistent
And since original and evaluated points might also be in completely
different positions, we also need to draw connecting lines between those
editpoints to not have them float in thin air. For drawing these in
editmode, a simple polyline was chosen (instead of drawing lines in a
resolution that is take from the old particle system -- which is not
depending on points even but has a hardcoded resolution that can only be
upped by the hair_subdiv scene render setting)
- create appropriate batch and indexbuffer for this
- positions vertex buffer can be reused
- reuse particle edit shader (instead of curve edi shader) to get segment highlighting
Potentionally fixes T101889.
