Analyzer support for type arguments on annotations

[stereotype441]

(Parent issue #44917)

This issue tracks the analyzer work necessary to support type arguments on annotations, for example:

@TypeHelper<int>(42, "The meaning")

For justification and additional planning details, please see:

• The feature request in the language issue tracker: Allow generic metadata annotations language#1297
• The feature specification: https://github.com/dart-lang/language/blob/master/accepted/future-releases/small-features-21Q1/feature-specification.md
• The implementation plan: https://github.com/dart-lang/language/blob/master/accepted/future-releases/small-features-21Q1/implementation-plan.md
• The implementation plan PR: Add feature specification and implementation plan for small features for Q1 of 2021 language#1417

[scheglov]

@leafpetersen @eernstg Are we allowed to combine generic metadata and generic functions as type arguments? Is this valid code?

class A<T> {
  const A();
}

@A<U Function<U>()>()
void f() {}

Or with inference?

class A<T> {
  const A(T _);
}

@A(g)
void f() {}

U g<U>() => throw 0;

[eernstg]

I see no reason to make that combination an error, whether inferred or written explicitly.

[scheglov]

AFAIK this is done.

[leafpetersen]

#45579

[scheglov]

#45579 was fixed.