[region-isolation] Refactor out the Region analysis from TransferNonSendable.

NFCI. This is just a pure refactor of the analysis part of TransferNonSendable
into a separate SIL level analysis so it can be reused by other passes.

The reason that I am committing this earlier is that I am working concurrently
on other patches that change TransferNonSendable itself and I want to avoid
issues when rebasing those patches. Getting this patch into tree earlier avoids
that.

This is in preparation for adding a new flow sensitive initialization pass that
combines region based analysis with the current flow sensitive isolation's
diagnostic emitter. The idea is that we want to preserve the diagnostics from
that pass rather than try to make our own as an initial step.

Author: gottesmm

include/swift/SILOptimizer/Analysis/Analysis.def

@@ -46,5 +46,6 @@ SIL_ANALYSIS(RCIdentity)
 SIL_ANALYSIS(TypeExpansion)
 SIL_ANALYSIS(PassManagerVerifier)
 SIL_ANALYSIS(DeadEndBlocks)
+SIL_ANALYSIS(Region)
 
 #undef SIL_ANALYSIS