Change default completor from regexp to type-completor if RUBY_VERSION>=3.4

[tompng]

In Ruby >= 3.4, ReplTypeCompletor is a bundled gem, installed by default.
This pull request changes the default completor to type-completor if RUBY_VERSION >= 3.4.
If ReplTypeCompletor is not available (not installed or not added to Gemfile), fallbacks to regexp-baased completion.
The default isstill :regexp if RUBY_VERSION < 3.4

Run with bundler

With bundler and when repl_type_completor is not added to Gemfile, IRB will use regexp-based completion.
IRB shows warning message only If --type-completor or IRB.conf[:COMPLETOR] = :type is explicitly specified.

$ ruby -v
ruby 3.4.0dev

$ irb
irb(main):001> irb_info
(TypeCompletor)

$ echo "gem 'irb', path: 'path/to/irb'" > Gemfile

$ bundle exec irb
(no waarning)
irb(main):001> irb_info
(RegexpCompletor)

$ bundle exec irb --type-completor
TypeCompletor requires `gem repl_type_completor`: cannot load such file -- repl_type_completor
irb(main):001> irb_info
(RegexpCompletor)

Restriction with rdbg

ReplTypeCompletor uses background thread to load RBS type information which could take time.
Debug gem stops all other threads, so if IRB enters debug mode before loading RBS completes, type completor can't use type information.
Even without type information, type completor can still complete as good or better than regexp-based completion.

[st0012]

Since repl_type_completor only has ~64k downloads atm, this means almost all IRB sessions after this change will trigger a LoadError unnecessarily. And at the same time, this change isn't actually making more people use repl_type_completor. It simply saves the existing users the need to configure it.

IMO the right solution here is to propose making repl_type_completor a bundled gem. And only until that happens, we make it a default for IRB with a Ruby version check as older Ruby versions still won't have it installed by default.

[tompng]

ReplTypeCompletor is added to bundled gem now 🎉 I updated the pull request description.

with a Ruby version check

Looks nice, added

[st0012]

Let's give it a try 🎉

[ima1zumi]

LGTM! 🚀