Use Snapper generator for RDoc

[andyw8]

To match ruby-lsp, based on Shopify/ruby-lsp#1384.

[andyw8]

Looking into this failure:

ruby-lsp-rails andyw8/rdoc-snapper % bundle exec rake rdoc                   
rake aborted!
LoadError: cannot load such file -- /Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/markdown (LoadError)
/Users/andyw8/.gem/ruby/3.3.0/gems/zeitwerk-2.6.13/lib/zeitwerk/kernel.rb:34:in `require'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/text.rb:24:in `<module:Text>'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/text.rb:11:in `<top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/gems/zeitwerk-2.6.13/lib/zeitwerk/kernel.rb:34:in `require'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/code_object.rb:30:in `<class:CodeObject>'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/code_object.rb:28:in `<top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/gems/zeitwerk-2.6.13/lib/zeitwerk/kernel.rb:34:in `require'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/generator/markup.rb:60:in `<top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/generator/darkfish.rb:7:in `require_relative'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/generator/darkfish.rb:7:in `<top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/rdoc.rb:561:in `require_relative'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/rdoc.rb:561:in `<top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/gems/zeitwerk-2.6.13/lib/zeitwerk/kernel.rb:34:in `require'
/Users/andyw8/.gem/ruby/3.3.0/bundler/gems/rdoc-dbabc13c8cee/lib/rdoc/task.rb:251:in `block in define'
/Users/andyw8/.gem/ruby/3.3.0/gems/rake-13.1.0/exe/rake:27:in `<top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/cli/exec.rb:58:in `load'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/cli/exec.rb:58:in `kernel_load'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/cli/exec.rb:23:in `run'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/cli.rb:451:in `exec'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/vendor/thor/lib/thor/command.rb:28:in `run'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/vendor/thor/lib/thor.rb:527:in `dispatch'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/cli.rb:34:in `dispatch'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/vendor/thor/lib/thor/base.rb:584:in `start'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/cli.rb:28:in `start'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/exe/bundle:28:in `block in <top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/lib/bundler/friendly_errors.rb:117:in `with_friendly_errors'
/Users/andyw8/.gem/ruby/3.3.0/gems/bundler-2.5.6/exe/bundle:20:in `<top (required)>'
/Users/andyw8/.gem/ruby/3.3.0/bin/bundle:25:in `load'
/Users/andyw8/.gem/ruby/3.3.0/bin/bundle:25:in `<main>'
Tasks: TOP => rdoc => docs/created.rid
(See full trace by running task with --trace)

[andyw8]

^ It's related to the Ruby version, fixed by setting to 3.2 as we do in ruby-lsp.