This CL adds extra fields to RangeStmt that can be used when
desugaring into primitive assignment statements. This will allow the
frontend to wire up all of the RTTI necessary, pulling from
dictionaries as necessary.

Updates #53328.

Change-Id: Iab0e3029ff18c947782ff24f71ef20b2b5cb8305
Reviewed-on: https://go-review.googlesource.com/c/go/+/415518


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