[rs4gc] avoid insert base computation instructions for deopt uses

If we have a value live over a call which is used for deopt at the call, we know that the value must be a base pointer. We can avoid potentially inserting IR to materialize a base for this value.

In it's current form, this is mostly a compile time optimization.   Building the base pointer graph (and then optimizing it away again) is a relatively expensive operation.  We also sometimes end up with better codegen in practice - due to failures in optimizing away the inserted base pointer propogation - but those are optimization bugs we're fixing concurrently.

The alternative to this would be to extend the base pointer inference with the ability to generally reuse multiple-base input instructions (phis and selects).  That's somewhat invasive and complicated, so we're defering it a bit longer.

Differential Revision: https://reviews.llvm.org/D97885