Add Ruby LSP support for VSCode (and possibly others)

[lloeki]

What does this PR do?

• Add a :dev Gemfile group for development-oriented gems.
• Add the ruby-lsp gem to that group.
• Remove the gem/group for appraisals.
• Suggest the Ruby LSP VSCode extension for this workspace.

Motivation:

This gem is used by the VSCode Ruby LSP extension from Shopify, and possibly other IDEs as well. Having it in the Gemfile for development provides a good out-of-the-box experience.

Additional Notes:

A few other extensions are recommended as well:

• EditorConfig: since we use that
• Steep and RBS: the official extensions

The suggestion should only pop up once and the user is free to install or dismiss.

How to test the change?

Using VS Code with the Ruby LSP extension should provide an immediate OOTB experience that uses the LSP.

If not installed already, the extension should be suggested by VSCode as a recommendation, which is also free to be dismissed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.91%. Comparing base (b428d21) to head (81c3037).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3777   +/-   ##
=======================================
  Coverage   97.91%   97.91%           
=======================================
  Files        1246     1246           
  Lines       74999    74999           
  Branches     3627     3627           
=======================================
+ Hits        73434    73435    +1     
+ Misses       1565     1564    -1     

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[anmarchenko]

I use the same gem and VSCode extension for datadog-ci-rb, it works great