Run some optimization passes before lowering the code, to allow for a
simpler compiler.

Current passes:
- Exhaustively inline functions
- Apply and freeze specialization constants

I expect this set of passes will change somewhat as the
compiler evolves. We may want to stop inlining at some point.

Bug: b/124058197
Bug: b/124056625

Change-Id: Ib2a3dc2d2599449d45ac7ebb1de107deba8eb2c3
Reviewed-on: https://swiftshader-review.googlesource.com/c/24288Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>