Static Analyzer Diagnostics: Kill the addVisitorCreator(callbackTy, void*) API in favor of addVisitor(BugReporterVisitor*).

1) Create a header file to expose the predefined visitors. And move the parent(BugReporterVisitor) there as well.

2) Remove the registerXXXVisitor functions - the Visitor constructors/getters can be used now to create the object. One exception is registerVarDeclsLastStore(), which registers more then one visitor, so make it static member of FindLastStoreBRVisitor.

3) Modify all the checkers to use the new API.

llvm-svn: 138126