RFR: 8367536: Change RBTree to use C++17 features [v4]

[Casper Norrbin]

> Hi everyone,
> 
> C++17 lets us tidy up som of the ugly templating done in the red-black tree. We can replace the `std::false_type`/`std::true_type` tricks used to discover comparator and verifier signatures with the new `std::is_invocable(_r_v)`, and most of the overload/SFINAE noise can disappear thanks to `if constexpr`.
> 
> We can now write one-liners such as:
> ```c++
> static constexpr bool HasKeyComparator = std::is_invocable_r_v<RBTreeOrdering, decltype(&CMP::cmp), K, K>;
> 
> 
> and then select the right branch with
> ```c++
> if constexpr (HasKeyComparator<CMP>) { }
> 
> inside a single function instead of having several `ENABLE_IF` overloads.
> 
> This results in fewer lines, clearer intent, and more readable errors, while keeping behaviour identical.
> 
> Testing:
> - Oracle tiers 1-3

Casper Norrbin has updated the pull request incrementally with one additional commit since the last revision:

  Added clarifying note + change name to 'HasNodeVerifierImpl'

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/27260/files
  - new: https://git.openjdk.org/jdk/pull/27260/files/6f52cbf1..184b5fc5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27260&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27260&range=02-03

  Stats: 5 lines in 1 file changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27260.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27260/head:pull/27260

PR: https://git.openjdk.org/jdk/pull/27260