Add LifetimeDependence utilities

    - LifetimeDependence

    - VariableIntroducerUseDefWalker

    - LifetimeDependenceUseDefWalker

    - LifetimeDependenceDefUseWalker

Author: atrick

SwiftCompilerSources/Sources/Optimizer/Utilities/CMakeLists.txt

@@ -12,6 +12,7 @@ swift_compiler_sources(Optimizer
   Devirtualization.swift
   EscapeUtils.swift
   ForwardingUtils.swift
+  LifetimeDependenceUtils.swift
   OptUtils.swift
   OwnershipLiveness.swift
   SSAUpdater.swift