Implement method hierarchy through existing type hierarchy logic.

[rgrunber]

• The method hierarchy for a given method of some type is a subset of the type hierarchy where methods not implemented are filtered out

• I should add some test cases for this

[CsCherrYY]

Just played with the change and LGTM overall. Some questions:

1. Can we consider to change the view title? Currently it's always Class Hierarchy, since the client is able to know whether it's a method hierarchy, a title like Method hierarchy for ${methodName} would be better I think.
2. Should we show the supertypes of the first type who implement the method? e.g., type Object in your example. I tried in IntelliJ, Object is now shown there.
   

[rgrunber]

1. The display is done purely on the client side, so I modified that part to show Method Hierarchy or Subtype (Method) Hierarchy / Super (Method) Hierarchy when that's the case. In order to also display the method name I'll just need to add an extra field under data. the current method data is just a unique identifier to retrieve the IMethod but it can't really be nicely used to retrieve a human-readable name.
2. I've excluded java.lang.Object, except for the special case where the method being searched originates from there (eg. toString, equals, etc.). In those cases I think it's worth showing just for the sake of correctness.

Update: I've sent an additional method_name data field that contains a human-readable method name. It might be possible to parse from the handle identifier since the method name seems to be contained within the tilde (~) char, but I'm not sure if that always holds true. See https://github.com/eclipse-jdt/eclipse.jdt.core/blob/c4a6546b03ec2be75940407d0c583d8c0c0ad2f3/org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/SourceMethod.java#L87-L94 .

[CsCherrYY]

As for the human-readable name part, since we can get the IMethod either from the handle identifier or getMember(), how about directly using IMethod.getElementName()?

[rgrunber]

As for the human-readable name part, since we can get the IMethod either from the handle identifier or getMember(), how about directly using IMethod.getElementName()?

Yup, that's exactly what I've gone with (forgot to push the change).

[CsCherrYY]

LGTM!