[ruby/prism] Add error handling for missing `parser` gem in `Prism::Translation`

[ruby/prism] Add error handling for missing `parser` gem in `Prism::Translation`

Resolves https://github.com/ruby/prism/pull/2803.

This PR adds error handling for missing `parser` gem in `Prism::Translation`.

The `parser` gem is a required runtime dependency when using `Prism::Translation::Parser`.
But it is not required for other uses of Prism. To avoid unnecessary dependencies,
it is not added as a `runtime_dependency` in the prism.gemspec. Instead, if the dependency is missing,
instructions are given to add it to Gemfile.

## Before

```console
$ bundle exec ruby -e 'require "prism"; require "prism/translation/parser33"'
/Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `require': cannot load such file -- parser (LoadError)
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `block (2 levels) in replace_require'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser.rb:3:in `<top (required)>'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `require'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `block (2 levels) in replace_require'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser33.rb:6:in `<module:Translation>'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser33.rb:4:in `<module:Prism>'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser33.rb:3:in `<top (required)>'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `require'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `block (2 levels) in replace_require'
from -e:1:in `<main>'
```

## After

```console
$ bundle exec ruby -e 'require "prism"; require "prism/translation/parser33"'
Error: Unable to load parser. Add `gem "parser"` to your Gemfile.
```

https://github.com/ruby/prism/commit/4880aec22d