Adds sourcetext setting

[TheAngryByrd]

WHAT

🤖 Generated by Copilot at 3bdb122

This pull request adds a new experimental feature to the extension that allows users to select a different source text implementation for the F# language server. It updates the package.json file and the LanguageService module to support this feature.

🤖 Generated by Copilot at 3bdb122

The F# language server is great
But sometimes it can be too late
To update the text
So they added a flex
With a new option to change its state

✨🔧📄

WHY

ionide/FsAutoComplete#1123

HOW

🤖 Generated by Copilot at 3bdb122

• Add a new configuration option for choosing the source text implementation of the F# language server (link)
• Pass the value of the new option to the language server process as a command line argument (link, link)
• Add a newline at the end of package.json (link)