[Feature #19134]

This was introduced by b609bdeb5307e280137b4b2838af0fe4e4b46f1c
to suppress warnings. However these warngins were deleted by
beae6cbf0fd8b6619e5212552de98022d4c4d4d4. Therefore these codes
are not needed anymore.

Implementation for Language Server Protocol (LSP) sometimes needs token information.
For example both `m(1)` and `m(1, )` has same AST structure other than node locations
then it's impossible to check the existence of `,` from AST. However in later case,
it might be better to suggest variables list for the second argument.
Token information is important for such case.

This commit adds these methods.

* Add `keep_tokens` option for `RubyVM::AbstractSyntaxTree.parse`, `.parse_file` and `.of`
* Add `RubyVM::AbstractSyntaxTree::Node#tokens` which returns tokens for the node including tokens for descendants nodes.
* Add `RubyVM::AbstractSyntaxTree::Node#all_tokens` which returns all tokens for the input script regardless the receiver node.

[Feature #19070]

Impacts on memory usage and performance are below:

Memory usage:

```
$ cat test.rb
root = RubyVM::AbstractSyntaxTree.parse_file(File.expand_path('../test/ruby/test_keyword.rb', __FILE__), keep_tokens: true)

$ /usr/bin/time -f %Mkb /usr/local/bin/ruby -v
ruby 3.2.0dev (2022-11-19T09:41:54Z 19070-keep_tokens d3af1b8057) [x86_64-linux]
11408kb

# keep_tokens :false
$ /usr/bin/time -f %Mkb /usr/local/bin/ruby test.rb
17508kb

# keep_tokens :true
$ /usr/bin/time -f %Mkb /usr/local/bin/ruby test.rb
30960kb
```

Performance:

```
$ cat ../ast_keep_tokens.yml
prelude: |
  src = <<~SRC
    module M
      class C
        def m1(a, b)
          1 + a + b
        end
      end
    end
  SRC
benchmark:
  without_keep_tokens: |
    RubyVM::AbstractSyntaxTree.parse(src, keep_tokens: false)
  with_keep_tokens: |
    RubyVM::AbstractSyntaxTree.parse(src, keep_tokens: true)

$ make benchmark COMPARE_RUBY="./ruby" ARGS=../ast_keep_tokens.yml
/home/kaneko.y/.rbenv/shims/ruby --disable=gems -rrubygems -I../benchmark/lib ../benchmark/benchmark-driver/exe/benchmark-driver \
            --executables="compare-ruby::./ruby -I.ext/common --disable-gem" \
            --executables="built-ruby::./miniruby -I../lib -I. -I.ext/common  ../tool/runruby.rb --extout=.ext  -- --disable-gems --disable-gem" \
            --output=markdown --output-compare -v ../ast_keep_tokens.yml
compare-ruby: ruby 3.2.0dev (2022-11-19T09:41:54Z 19070-keep_tokens d3af1b8057) [x86_64-linux]
built-ruby: ruby 3.2.0dev (2022-11-19T09:41:54Z 19070-keep_tokens d3af1b8057) [x86_64-linux]
warming up..

|                     |compare-ruby|built-ruby|
|:--------------------|-----------:|---------:|
|without_keep_tokens  |     21.659k|   21.303k|
|                     |       1.02x|         -|
|with_keep_tokens     |      6.220k|    5.691k|
|                     |       1.09x|         -|
```

NEW_PREEXE has not been used since 52a5f76e8b1ab02ee6e259a7cff9e8c5475744e8

By this change, syntax error is recovered smaller units.
In the case below, "DEFN :bar" is same level with "CLASS :Foo"
now.

```
module Z
  class Foo
    foo.
  end

  def bar
  end
end
```

[Feature #19013]

[Misc #18891]

This `NODE` type was used in pre-YARV implementation, to improve
the performance of assignment to dynamic local variable defined at
the innermost scope.  It has no longer any actual difference with
`NODE_DASGN`, except for the node dump.