Regression in recent undo system changes,
This caused T55048.
When each mode had its own undo stack it was important
to initialize it when entering edit-mode.
- Add blentranslation `BLT_*` module.
- moved & split `BLF_translation.h` into (`BLT_translation.h`, `BLT_lang.h`).
- moved `BLF_*_unifont` functions from `blf_translation.c` to new source file `blf_font_i18n.c`.
Changed curve active point from pointer to index. Allows curve active point to be saved to file and retained between modes for free. Also some small optimisations by removing pointer look up code.
- Made active point access functions into BKE API calls.
- Fixes operators where curve de-selection resulted in unsel-active point.
- Split curve delete into 2 functions
* deselect all no longer leaves an active point
* the most recently added spline becomes the active one
* on successful duplicate/delete the active point and active spline are reset
curves and metaballs now behave the same as meshes wrt grid scaling.
remove WM_operator_view3d_distance_invoke(), and replace with a function called from exec which initializes defaults, this way operators can have their own invoke functions.
