Some users are discussing that the current refit algorithm does not
produce the expected results when using Apply Base, while others expect
this feature to create a base mesh that will look like the Multires grid
displacement when being subdivided again.
This patch splits the Apply Base operator into Apply Base and Refit Base.
Apply base will not refit the mesh, creating the same final result as
applying the subdivisions and using Rebuild Subdivisions. Refit Base is
the equivalent of the previous Apply Base, which will deform the base
mesh and refit.