Trim analyzer hole for new constraint in constructor

[sbomer]

Extracted from #108507

[RequiresUnreferencedCode("")]
class A;

class B<T> where T : new();

class C : B<A>
{
    public C()
    { // No warning from the analyzer!
    }
}

Note that the following example does warn:

[RequiresUnreferencedCode]
class Requires {}

class Derived : Requires
{
    public Derived // warning IL2026
    {
    }
}

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