Remove static variable for global_terms_enable to allow for unit tests

[jeremyfelt]

From @boonebgorges in #31149:

global_terms_enabled() stores the check in a static, which makes it impossible to toggle for the purposes of the unit tests. This was introduced in [14344] in what was, I assume, an attempt to optimize the function. @nacin do you have a problem if I roll this back and filter it every time the function is called? global_terms_enabled() is not called anywhere on the front end in core, and nowhere that I've found yet in the plugin repo, so I don't foresee any serious performance issues.

31149.diff makes the necessary changes and adds unit tests to address #31149

[jeremyfelt]

In 32064:

Avoid an unexpected object error when syncing global terms

Pass the expected single value, rather than object, when recursively calling global_terms().

Props hauvong.

See #31914, Fixes #31149.

[obenland]

No movement in 4.3, maybe in a future release.

[helen]

What do we need here - a consult from somebody with knowledge of the history or an eye on the implications of this?