Rename some mutable closure types for consistency

Description taken from the diff:

SMALL_MUT_ARR_PTRS_FROZEN0 -> SMALL_MUT_ARR_PTRS_FROZEN_DIRTY
SMALL_MUT_ARR_PTRS_FROZEN -> SMALL_MUT_ARR_PTRS_FROZEN_CLEAN
MUT_ARR_PTRS_FROZEN0 -> MUT_ARR_PTRS_FROZEN_DIRTY
MUT_ARR_PTRS_FROZEN -> MUT_ARR_PTRS_FROZEN_CLEAN

Naming is now consistent with other CLEAR/DIRTY objects (MVAR, MUT_VAR, MUT_ARR_PTRS).

(alternatively we could rename MVAR_DIRTY/MVAR_CLEAN etc. to MVAR0/MVAR)

Removed a few comments in Scav.c about FROZEN0 being on the mut_list because it's now clear from the closure type.

Trac metadata

Trac field	Value
Version	8.4.3
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
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