Cover RSP-indexed accesses in frame optimization

Summary:
Add a new dataflow analysis to recover the value of RSP at a
given point of the program. This value is expressed as an offset from
the CFA. Use this information to detect redundant load in memory
accesses performed via RSP as well, not only RBP as done previously.
Bail when RSP value (as an offset of the CFA) can't be reliably
determined with a simple dataflow analysis.

(cherry picked from FBD4372261)