Fix range handling for code completion in interpolated strings

[kojo12228]

WHAT

🤖 Generated by Copilot at a165188

This pull request fixes a bug in the completion logic for interpolated strings and adds tests to verify the fix. It modifies the UntypedAstUtils.fs file to handle overlapping ranges of interpolated string parts, and the CompletionTests.fs and Script.fsx files to add two test cases using the List module.

🤖 Generated by Copilot at a165188

Fix interpolated
Completion logic bug in
Autumn of F Sharp

🐛🧪📝

WHY

The range for the DiscardAfterMissingQualificationAfterDot overlaps with the rest of the string in $"{List.}", but doesn't in $"{ List. }". Potentially the real fix should be a change to that range instead, but I don't know enough about the AST to know whether that is the right call.

HOW

🤖 Generated by Copilot at a165188

• Fix bug in completion logic for interpolated strings by adding index to parts list and checking previous part range (link)
• Add test cases for completion in interpolated strings using testCaseAsync and Script.fsx (link, link)

Related to #962, but doesn't completely fix it.

[baronfel]

Thanks for this! And especially thanks for adding tests :)

[TheAngryByrd]

Thank you!!