[analyzer] Utility to match function calls.

This patch adds a small utility to match function calls. This utility abstracts away the mutable keywords and the lazy initialization and caching logic of identifiers from the checkers. The SimpleStreamChecker is ported over this utility within this patch to show the reduction of code and to test this change.

Differential Revision: http://reviews.llvm.org/D15921

llvm-svn: 258572