[analyzer] Previously, we were passing to CheckerContext enough info to...

[analyzer] Previously, we were passing to CheckerContext enough info to construct ProgramPoint and it would pass it to NodeBuilder, which in turn would construct the ProgramPoint. Simplify it by just passing the ProgramPoint to CheckerContext. The ProgramPoint can only change if a checker tags it, in which case, we create a copy with the given tag.

(A step closer to making CheckerContext work with all node builders, not only StmtNodeBuilder.)

llvm-svn: 141417