[Sema] Remove a -Wrange warning from -Wall

During the review of D73007 Aaron Puchert mentioned
`warn_for_range_variable_always_copy` shouldn't be part of -Wall since
some coding styles require `for(const auto &bar : bars)`. This warning
would cause false positives for these users. Based on Aaron's proposal
refactored the warnings:

* -Wrange-loop-construct warns about possibly unintended constructor
  calls. This is part of -Wall. It contains
  * warn_for_range_copy: loop variable A of type B creates a copy from
    type C
  * warn_for_range_const_reference_copy: loop variable A is initialized
    with a value of a different type resulting in a copy
* -Wrange-loop-bind-reference warns about misleading use of reference
  types. This is not part of -Wall. It contains
  * warn_for_range_variable_always_copy: loop variable A is always a copy
    because the range of type B does not return a reference

Differential Revision: https://reviews.llvm.org/D73434