Swift Optimizer: add EscapeInfo, a new utility for escape analysis

It’s a replacement for the old `EscapeAnalysis`, implemented in Swift (instead of C++) and with a much simple design and implementation.
While the old EscapeAnalysis builds a connection graph, the new EscapeInfo just performs a simple def-use and use-def walk in the SIL.
The EscapeInfo does not need to analyze the whole function (like the EscapeAnalysis does), but just the relevant value which is inspected. Therefore EscapeInfo is not an `Analysis` which caches its result across optimization passes - it’s not needed.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Utilities/CMakeLists.txt

@@ -7,4 +7,5 @@
 # See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 
 swift_compiler_sources(Optimizer
+  EscapeInfo.swift
   OptUtils.swift)