`viewops_data_alloc` allocates and stores some pointers in
`ViewOpsData` while `viewops_data_create` reuses already stored
pointers and also stores others in `ViewOpsData`.
The similar names and usages can confuse and in this case it also
creates a dependency on the order in which these functions are called.
Merging these functions simplifies usage and deduplicates code.
The view3d_edit.c file is already getting big (5436 lines) and mixes
operators of different uses.
Splitting the code makes it easier to read and simplifies the
implementation of new features.
Differential Revision: https://developer.blender.org/D13976