skip liquify transforms for viewport changes

[dterrahe]

Simpler alternative to #19243

I believe this also fixes the infinite refresh loop you got because dt_dev_pixelpipe_process would store a transformed location and dt_view_paint_surface would compare it to the untransformed one it requested and immediately rerequest it.

Also dedupped (most of) _dev_distort_back/transform_locked

[ralfbrown]

Looks good on a quick skim (better than my proposal). The new tag should have a different name though - I propose either IOP_TAG_GEOMETRY or IOP_TAG_NODISTORT. Iops with the new tag aren't disabling the geometry-only transform, they can be viewed as either enabling it or disabling the full distortion transform.

[TurboGit]

Works for me, a minor comment about naming of new enum.

[TurboGit]

Thanks!