[AAPointerInfo] rearrange code in preparation for further changes

AAPointerInfoFloating::updateImpl
  Move the member function definition out of its class before modifying it.

translateAndAddState
  Split the function definition into two along the FromCallee boolean argument.

handleAccess
  This should only be called when Size is not known. In other cases, replaced
  with a direct call to addAccess.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D138645