chore: Add support for derivedClasses metadata when implements interfaces

[filzrev]

This PR intended to fix a part of issue that is reported at #2531

Currently docfx generate derivedClasses metadata when inherited from class.
But derivedClasses metadata is not outputted for interface implements.

This PR add derivedClasses support for interfaces.

Additionally, Replace dictionary lookup logics to use CollectionsMarshal.GetValueRefOrAddDefault
to reduce dictionary double-lookup costs.

Test
I've manually confirmed derivedClasses metadata generation with following sample code.
And confirmed metadata is generated as expected.

namespace BuildFromProject;

public interface ISample{}

public abstract class SampleClassBase :ISample {}

public class Sample01 :ISample
{
    public int AAA{get;set;}
}

public class Sample02: ISample
{
    public int BBB{get;set;}
}

public class Sample03: SampleClassBase
{
    public int BBB{get;set;}
}

TODO
Currently derivedClasses metadata information is not rendered for interface HTML page.
It need to modify docfx templates also (by another PR)