Fallback to latest known Ruby if no .ruby-version is found

[vinistock]

Motivation

Completes a significant part of handling missing .ruby-version for #2793

If the user doesn't have a .ruby-version in their project or in any parent directories, then we can try to fallback to the latest known Ruby available.

Note: this PR doesn't handle the aspect of having a .ruby-version configured to a Ruby that's not installed. I'll follow up with that later.

Implementation

To avoid having this behaviour be surprising, I used a progress notification with a 5 second delay warning the user that we are going to try falling back to the latest known Ruby. If they don't do anything, we search for the Ruby installation and launch.

If the user clicks cancel, then we stop everything and offer them 3 options:

1. Create a .ruby-version file in a parent directory. Here we use a quick pick to list all known rubies and create the file for them using what they select
2. Manually configure a global fallback Ruby installation for the LSP
3. Shutdown

Automated Tests

Added automated tests for two scenarios. I haven't figured out if it's possible to trigger the cancellation in a test even with a stub, so I failed to create tests for those cases.

If you have an idea about how to fake the cancellation of the progress notification, please let me know!

[vinistock]

• Fallback to latest known Ruby if no .ruby-version is found #2836 👈 (View in Graphite)
• Allow individual version managers to trigger manual Ruby selection #2835
• main

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[andyw8]

As discussed:

• Increase the time we show the initial dialog (to 10s or 15s)
• Since the labels are being truncated, let's add a description above so that we can use more concise labels.
• Let's allow the user to choose which folder .ruby-version is written to, rather the parent, to avoid potential problems running other Ruby projects on their system.
• Change configure messsage to "Configure global fallback or workspace specific Ruby for Ruby LSP?"
• Remove 'shutdown' button (can use X instead)
• Change "The Ruby LSP requires a Ruby version to launch. You can define a fallback by adding a .ruby-version to a parent directory or by configuring a fallback" to make it clear that one setting is for your system, the other is only for the Ruby LSP extension, e.g.:

"The Ruby LSP requires a Ruby version to launch. You can define a system or Ruby LSP fallback to use"

Buttons: [System fallback] [Ruby LSP fallback]
(adjust placeholders/title as necessary)