Add an optional init function which operators
An alternative to [0] which missed Python API support (causing #140451).
While that could be resolved, tracking which "slots" have been set
would have to be flagged on every map/hash insertion which seems
excessive and is prone to bmesh operators failing if the flag is ever
missed. Prefer a simpler init function so dissolve edges doesn't have
a zero threshold.
Also support multi-line comment blocks in the generated API docs.
[0]: bd3a66a416
4dba0113fd