Added Subtype Analyzer

[mitchcapper]

Find classes/interfaces that directly subtype the analyzed class/interface.

Technically I generally only use the new-ilspy branch for non-debugging but this applied fine to master as well so submitting here.

I felt directly subtyping was the best way to go rather than any that implement/subtype felt natural with the normal behavior of the analyze panel and avoids too many downstream results for popular classes/interfaces.

Not sure if the copyright header is correct.

[ElektroKill]

Some minor code style issues and a few edge cases to handle in the checks!

I also think hat calling the node Subtypes would be better than calling it Subtyped By which in my opinion sounds a bit weird. Let me know what you think of this!

[mitchcapper]

All changes made. Let me know if you want the class renamed from SubtypedBy in addition to just the language string.

This code could be executed many times. Avoid using LINQ and instead use a normal iterative for loop. It doesn't make that much of a difference in most cases but we should keep consistent with the rest of dnSpy

I think I styled it after this so depending on how much consistency you want you may want to update: https://github.com/dnSpyEx/dnSpy/blob/feature/new-ilspy/Extensions/dnSpy.Analyzer/TreeNodes/InterfaceEventImplementedByNode.cs#L82

[ElektroKill]

This code could be executed many times. Avoid using LINQ and instead use a normal iterative for loop. It doesn't make that much of a difference in most cases but we should keep consistent with the rest of dnSpy

I think I styled it after this so depending on how much consistency you want you may want to update: feature/new-ilspy/Extensions/dnSpy.Analyzer/TreeNodes/InterfaceEventImplementedByNode.cs#L82

Some of the analyzer code is very old and based on old ILSpy analyzer source code. It hasn't been touched for years and could use some modernization but I'm not touching it for now since it's not really causing any problems yet.

[mitchcapper]

all set

[ElektroKill]

One last issue regarding naming. Otherwise LGTM!

[mitchcapper]

Change the data name to SubtypesTreeNode to better reflect its value.

I think we had a small miscommunication,

I am happy you are willing to own your share of the blame on this miscommunication. You with your clear directions and me with my inability to read id say pretty 50/50.