add coarse-grain support on ARM

Split from #1551 as this is a big feature but is lower priority and thus may be delayed significantly from the core ARM port. Coarse-grain freezing, merging, and persisting has a lot of x86-specific code and will take significant effort to port.

Start by reading issue #1551 and the existing x86-specific coarse-grain freezing, merging, and persisting implementation. Map the ARM port's current scope and identify the related code and tests; done means those coarse-grain capabilities work on ARM.

Written by the indexing model from the issue text.