Cleanup profile reader classes to prepare for complex refactoring as propsed in D147740, continuing D148868
This is patch 2/n. This patch refactors CSNameTable and related things
The decision to move CSNameTable up to the base class is because a planned improvement (D147740) to use MD5 to lookup Functions/Context frames. In this case we want a unified data structure between contextless function or Context frames, so that it can be mapped by MD5 value. Since Context Frames can represent contextless functions, it is being used for MD5 lookup, therefore exposing it to the base class
Reviewed By: snehasish, wenlei
Differential Revision: https://reviews.llvm.org/D148872
776bb279d6