- Refactor tagging logic into a function to remove duplicate code
The two phases of tagging were identical logic just with the variables
and tag values swapped. This change ensures the two loops use matching
behavior.
- Adjust iteration to prevent restarting from the beginning of the mesh
after each island.
- Simplify and speed iteration tests.
testing to ensure v->e is non-null is redundant - verts with no edges
would never have passed `bm_vert_dissolve_fan_test` in the first
place, so can't be tagged as `VERT_INDEX_INIT`.
Re-testing `bm_vert_dissolve_fan_test(v)` is redundant - it was
checked above, and during tagging, the topology does not change.
Topology only changes later, after tagging is complete.
Therefore it's guaranteed to return the same result as the first time.
- Simplify loop logic, rename vars for clarity
offset and nth were constants, and depth was what causes alternation.
However none of that math is necessary - it can simply be done with
call order.
'seek_a' and 'seek_b' were renamed to what they actually are - lists
of verts that are tagged for collapse and ignore, respectively.
Further, by checking if any verts were tagged during the first
iteration pass, the second iteration pass can be avoided entirely if
it will perform no work.
Ref: !135212
80a38bb1e4