[release/10.0-rc1] Add trim analysis for implicit constructors

[github-actions]

Backport of #118755 to release/10.0-rc1

/cc @sbomer

Customer Impact

• Customer reported
• Found internally

A customer used our tooling while working on MVVM Toolkit, and was surprised to see a new trim warning show up during publish for an implicit constructor. The warning was expected to be caught by the analyzer.

Code like the following doesn't produce analyzer trim warnings even though it is calling an annotated constructor. But when publishing the app there is a warning B()'s call to A().

B b = new(); // No warnings here either

abstract class A
{
    [RequiresUnreferencedCode("blah")]
    public A()
    {
    }
}

// No warnings here
class B : A
{
}

Regression

• Yes
• No

Testing

This was a known analysis hole with existing analyzer test coverage. Updated the expected warning behavior for the analyzer tests.

Risk

Low. May introduce new build-time warnings for improperly annotated libraries, but the new warning is there for parity with publish-time warnings so this is mostly fixing a user experience problem (not a new class of warnings).

[jeffschwMSFT]

lgtm. please get a code review. we will take for consideration in 10 rc1

[ViktorHofer]

If this one should still go into RC1, please merge asap.