Swift Optimizer: add projection path DefUse/UseDef walkers

Introduces a set of protocols useful to perform def-use and use-def
traversals to find uses and definitions of values.

This logic was originally baked into `EscapeInfo` directly.
Here we extract it into general utilities, namely:
- `ValueDefUseWalker`: visit uses of a value walking down value-value projections/constructions.
- `AddressDefUseWalker`: visit uses of an address walking down addr-addr projections/constructions.
- `ValueUseDefWalker`: visit definitions of a value walking up value-value projections/constructions.
- `AddressUseDefWalker`: visit definitions of an address walking up addr-addr projections/constructions.

These utilities can then be used in other passes or to create
new utilities by composing them. For example to find a definition
passing through both address projections and value extractions,
it's enough to implement a visitor conforming to both
`AddressUseDefWalker` and `ValueUseDefWalker`.

Author: Anxhelo Xhebraj

SwiftCompilerSources/Sources/Optimizer/Utilities/CMakeLists.txt

@@ -8,4 +8,6 @@
 
 swift_compiler_sources(Optimizer
   EscapeInfo.swift
-  OptUtils.swift)
+  OptUtils.swift
+  WalkUtils.swift
+)