[analyzer] introduce getSVal(Stmt *) helper on ExplodedNode, make sure the helper is used consistently

In most cases using
`N->getState()->getSVal(E, N->getLocationContext())`
is ugly, verbose, and also opens up more surface area for bugs if an
inconsistent location context is used.

This patch introduces a helper on an exploded node, and ensures
consistent usage of either `ExplodedNode::getSVal` or
`CheckContext::getSVal` across the codebase.
As a result, a large number of redundant lines is removed.

Differential Revision: https://reviews.llvm.org/D42155

llvm-svn: 322753
diff --git a/clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
index 40217bd..0497ee7 100644
--- a/clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
@@ -94,7 +94,7 @@
   // FIXME: Handle multi-dimensional VLAs.
   const Expr *SE = VLA->getSizeExpr();
   ProgramStateRef state = C.getState();
-  SVal sizeV = state->getSVal(SE, C.getLocationContext());
+  SVal sizeV = C.getSVal(SE);
 
   if (sizeV.isUndef()) {
     reportBug(VLA_Garbage, SE, state, C);