Auto merge of #113915 - cjgillot:ssa-call, r=tmiasko

Also consider call and yield as MIR SSA.

The SSA analysis on MIR only considered `Assign` statements as defining a SSA local.
This PR adds assignments as part of a `Call` or `Yield` terminator in that category.

This mainly allows to perform CopyProp on a call return place.

The only subtlety is in the dominance property: the assignment is only complete at the beginning of the target block.

Author: bors