Partial properties: misc compiler layer work

[RikkiGibson]

Test plan: #73090
Related: dotnet/csharplang#8131

• Doc comments
• Extern scenarios
• LangVersion
• compilation events

[RikkiGibson]

@jcouv @333fred for review

[jcouv]

Consider validating IsExtern in other extern tests below (like Extern_02)

[jcouv]

nit: We commonly do bool inSource = module is SourceModuleSymbol; to avoid the extra parameter, thus allowing for symbolValidator : verify, sourceSymbolValidator: verify

[RikkiGibson]

I'll keep this in mind for future tests

[jcouv]

LGTM Thanks (iteration 7) modulo RegularNext in LangVer test

[333fred]

Only one small comment, otherwise LGTM.

[333fred]

I wonder if this existing check is actually correct for partial symbols that can't skip implementation?

[RikkiGibson]

I would be concerned about a scenario like this: (SharpLab for analogous method scenario)

public partial class C {
    void M0()
    {
        _ = Prop; // on hover do we see the doc comment?
    }
    
    /// <summary>Property comment</summary>
    partial int Prop { get; } // no impl
}

Thankfully I think the !_isForSingleSymbol logic on line 288 (at time of writing this comment) ensures that Quick Info does show a doc comment here. We could add a test.

[333fred]

Should add soem doc tests when we're missing an implementation member.

[jcouv]

LGTM Thanks (iteration 10)

[RikkiGibson]

For context. Something about my testing workflow was causing trailing whitespace on lines of the test to be lost, but our asserts were sensitive to that whitespace. I was finding it really frustrating to dig up that whitespace (basically had to go into the debugger and poke at the actual documentation string) so went ahead and started using a whitespace-insensitive comparison (though still line-sensitive) for a few of the tests.