[analyzer] Refactor EndOfFunctionNodeBuilder.

-Introduce EndOfFunctionNodeBuilder::withCheckerTag to allow it be "specialized" with a
 checker tag and not require the checkers to pass a tag.
-For EndOfFunctionNodeBuilder::generateNode, reverse the order of tag/P parameters since
 there are actual calls that assume the second parameter is ExplodedNode.

llvm-svn: 126332