Also split out helpers for testing matcher ranges (types whose
begin/end/empty/etc require ADL lookup, types whose iteration
uses iterator + sentinel pair, etc) into their own file.
This is primarily done to support new `std::*_ordering` types,
but the refactoring also supports any other type with this
property.
The compilation overhead is surprisingly low. Testing it with
clang on a Linux machine, compiling our SelfTest project takes
only 2-3% longer with these changes than it takes otherwise.
Closes#2555
