[ruby/prism] Support `itblock` for `Prism::Translation::Parser`

## Summary

`itblock` node is added to support the `it` block parameter syntax introduced in Ruby 3.4.

```console
$ ruby -Ilib -rprism -rprism/translation/parser34 -e 'buffer = Parser::Source::Buffer.new("path"); buffer.source = "proc { it }"; \
                                                      p Prism::Translation::Parser34.new.tokenize(buffer)[0]'
s(:itblock,
  s(:send, nil, :proc), :it,
  s(:lvar, :it))
```

This node design is similar to the `numblock` node, which was introduced for the numbered parameter syntax in Ruby 2.7.

```
$ ruby -Ilib -rprism -rprism/translation/parser34 -e 'buffer = Parser::Source::Buffer.new("path"); buffer.source = "proc { _1 }"; \
                                                      p Prism::Translation::Parser34.new.tokenize(buffer)[0]'
s(:numblock,
  s(:send, nil, :proc), 1,
  s(:lvar, :_1))
```

The difference is that while numbered parameters can have multiple parameters, the `it` block parameter syntax allows only a single parameter.

In Ruby 3.3, the conventional node prior to the `it` block parameter syntax is returned.

```console
$ ruby -Ilib -rprism -rprism/translation/parser33 -e 'buffer = Parser::Source::Buffer.new("path"); buffer.source = "proc { it }"; \
                                                      p Prism::Translation::Parser33.new.tokenize(buffer)[0]'
s(:block,
  s(:send, nil, :proc),
  s(:args),
  s(:send, nil, :it))
```

## Development Note

The Parser gem does not yet support the `it` block parameter syntax. This is the first case where Prism's node design precedes that of the Parser gem.
When implementing https://github.com/whitequark/parser/issues/962, this node design will need to be taken into consideration.

https://github.com/ruby/prism/commit/c141e1420a

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