dresources: document why RemapState is skipped when types match

[denik]

Adapter.RemapState returns the remote unchanged when a resource has no RemapState method. That's only correct because validate() requires remoteType == stateType in that case, but the fallback branch didn't say so. Add a comment.

This pull request and its description were written by Isaac.

[eng-dev-ecosystem-bot]

Integration test report

Commit: a1c5adb

Run: 35616056575

	Env	🔄​flaky	✅​pass	🙈​skip	Time
✅​	aws linux		276	15	6:29
✅​	aws windows		278	13	5:58
✅​	azure linux		275	15	5:59
✅​	azure windows		277	13	5:31
✅​	gcp linux		276	15	6:16
🔄​	gcp windows	1	277	13	6:12

	Test Name	gcp windows
🔄​	TestAccept	🔄​f

Top 3 slowest tests (at least 2 minutes):

duration	env	testname
5:55	aws windows	TestAccept
4:32	azure windows	TestAccept
2:39	gcp windows	TestAccept