Add new ConversionKind to IsImplicitConversion test

[ryzngard]

Fixes #34984

UnsetConversionKind was added by this commit but the switch statement wasn't updated.

[ryzngard]

Is there a place I can add tests? Just adding this code to our CodeAction tests didn't trigger the bug, but likely somewhere in the compiler layer there's a good place to add one.

[jcouv]

@ryzngard For testing, based on what I can see in the issue (stack trace), you need to get the conversion that is causing problems (likely from a semantic model call) and check IsExplicit on it. You need to debug the IDE code to figure out where the conversion came from (what syntax, regular or speculative semantic model, ...).

In terms of where to add the new compiler test(s), I see that Conversion.IsExplicit seems particularly covered in GetSemanticInfoTests.cs. Seems a good place.

[jcouv]

Marked PR as "private" for now. Please ping if you have any other questions, or once ready for review after test is added. Thanks

[ryzngard]

@jcouv test added to cover this bug, should be ready for review

[jcouv]

UnsetConversion [](start = 36, length = 15)

Feels like there is a bigger issue here. I'd expect the conversion to be Conversion.NoConversion (and Exists to be false).

I think that was changed by PR #33648 which introduced UnsetConversion, but not intentionally.
Let's discuss with @gafter

[ryzngard]

I'm going to continue with this PR as is to fix the crash. I've filed #35918 to track a deeper fix if needed.

[ryzngard]

@jcouv @RikkiGibson please take another look at this. I've opened a separate issue for the open concern #35918

[gafter]

@jcouv and @agocke are out of the office right now so it may take a little while to complete this review.

[333fred]

LGTM (commit 5)

[gafter]

@ryzngard The compiler team requires two reviews before merging. Generally speaking you should let each team merge reviews for code maintained by that team. Hopefully @jcouv will be able to look at this on Tuesday. I am not going to revert this, but it is possible there will be more work on the basis of his review.

[ryzngard]

@gafter my apologies. I'll remember that for the future.