Trim analyzer C# 14 support

[jtschuster]

The trim analyzer hasn't been tested with new C# 14 features to make sure it doesn't crash, report incorrect warnings, or miss warnings.

One issue is the analyzer doesn't recognize the 'field' keyword, and gives it UnknownValue for a dataflow value, resulting in a warning for the following code:

[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields)]
static Type MyType { get => field; } // Value returned from method 'MyType.get' can not be statically determined and may not meet 'DynamicallyAccessedMembersAttribute' requirements.

https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-14

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[jtschuster]

Began looking at this today, and it looks like the Microsoft.CodeAnalysis version used by the analyzer (and the latest version I could find) creates an IInvalidOperation for the syntax field.

Filed dotnet/roslyn#79201