With the recent sculpt refactor project prior to 4.3, the Sculpt undo
system was changed such that an individual `SculptUndoStep` would store
a single type on the `StepData` struct instead of storing individual
nodes that each had their own type.
This works for most operators supported by Sculpt Mode, however, the
`Apply Base` multires operator was dependent on needing to store both
Geometry and Position data.
To restore old functionality, this commit removes the need for storing
this Position data by instead forcing the object space Sculpt Mode
multires data to be flushed to the tangent space MDisp data prior to
saving the current geometry state so that it can be restored correctly.
This has the following benefits:
* We can continue to assume that Geometry steps represent full-mesh
changes and should require no further specialized processing.
* This better aligns with the future state of trying to flush this
multires data on a per-stroke basis instead of needing to wait unti
lthe user either quits or exits sculpt mode.
Pull Request: https://projects.blender.org/blender/blender/pulls/132569
c9ffd42417