[Bug #20736]

This commit switches the default parser to Prism. There are a
couple of additional changes related to this that are a part of
this as well to make this happen.

* Switch the default parser in parse.h
* Remove the Prism-specific workflow and add a parse.y-specific
  workflow to CI so that it continues to be tested
* Update a few test exclusions since Prism has the correct
  behavior but parse.y doesn't per
  https://bugs.ruby-lang.org/issues/20504.
* Skips a couple of tests on RBS which are failing because they
  are using RubyVM::AbstractSyntaxTree.of.

Fixes [Feature #20564]

```
  1) Error:
TestRubyLiteral#test_float:
ArgumentError: SyntaxError#path changed: "(eval at /home/chkbuild/chkbuild/tmp/build/20240527T050036Z/ruby/test/ruby/test_literal.rb:642)"->"(eval at /home/chkbuild/chkbuild/tmp/build/20240527T050036Z/ruby/test/ruby/test_literal.rb:642)"
```
https://rubyci.s3.amazonaws.com/s390x/ruby-master/log/20240527T050036Z.fail.html.gz

This commit simplifies warnings for hash keys duplication and when clause duplication,
based on the discussion of https://bugs.ruby-lang.org/issues/20331.
Warnings are reported only when strings are same to ohters.

As preparation for https://bugs.ruby-lang.org/issues/20205
making sure the test suite is compatible with frozen string
literals is making things easier.

We should pass `false` for `hash_key` for value nodes. Credits to
`@kddnewton` for noticing and bisecting.

```
$ ruby -e 'h = { __ENCODING__ => 1, __ENCODING__ => 2 }'
-e:1: warning: key #<Encoding:UTF-8> is duplicated and overwritten on line 1
```

`to_s` has the explict specification while `inspect` is often
vague.