[ENH]: Drop STOP codes?

[anntzer]

Problem

Matplotlib Paths can have a STOP code (https://matplotlib.org/stable/api/path_api.html#matplotlib.path.Path) which marks the end of a path but are otherwise unused; paths without STOP code are also supported.
I suspect that these are a artefact due to agg's implementation (i.e. agg emits them and we therefore also do).
While #28176 is technically not an issue because the behavior is as documented, it may help to just not emit these STOPs at all. I suspect this is just a matter of looking at all places where we return paths from Agg and clip out the last STOP code when it is present.
(We don't have to drop support for user passing them in, but could hide them in the documentation.)

Proposed solution

No response

[timhoffm]

Seems reasonable. It's still an API change that needs communication. There may be people out there, who knew they get a STOP node, so just dropped the last node. We cannot warn on that at runtime (with reasonable effort). Still the deprecation note should mention how to manually drop the last node if it's STOP to write code that is compatible across matplotlib versions.