[analyzer] Rework SValBuilder::evalCast function into maintainable and clear way

Summary: Refactor SValBuilder::evalCast function. Make the function clear and get rid of redundant and repetitive code. Unite SValBuilder::evalCast, SimpleSValBuilder::dispatchCast, SimpleSValBuilder::evalCastFromNonLoc and SimpleSValBuilder::evalCastFromLoc functions into single SValBuilder::evalCast.
This patch shall not change any previous behavior.

Differential Revision: https://reviews.llvm.org/D90157