add get_subsets_as_regions method to subset plugin, deprecate get_int… #11167

Job	Run time
Code style checks	16s
PEP 517	23s
Security audit	25s
Python 3.11 with coverage checking, all deps, and remote data	41m 8s
OS X - Python 3.12	11m 41s
Windows - Python 3.10	25m 19s
Python 3.12 with latest dev versions of key dependencies, and remote data	31m 19s
Python 3.11 with stable versions of dependencies and Roman	16m 7s
Upload Coverage	11s
	2h 6m 49s

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