RFR: JDK-8302324: Inheritance tree does not show correct type parameters/arguments

[Hannes Wallnöfer]

Please review a simple change to show the correct type parameters or arguments in the inheritance list in the class documentation header. The solution is simply to move the implementation of `Utils.getFirstVisibleSuperClass(...)` from the method with a `TypeElement` parameter to the one with a `TypeMirror` parameter, thereby preserving the type arguments.

I compared JDK API docs with and without this change, and the only change is that inheritance with generic superclasses is now rendered correctly. For instance, the inheritance list for `java.util.Properties` used to look like this:


java.lang.Object
    java.util.Dictionary<K,V>
        java.util.Hashtable<Object,Object>
            java.util.Properties

Now it is generated as follows:

java.lang.Object
    java.util.Dictionary<Object,Object>
        java.util.Hashtable<Object,Object>
            java.util.Properties

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Commit messages:
 - JDK-8302324: Inheritance tree does not show correct type parameters/arguments

Changes: https://git.openjdk.org/jdk/pull/12544/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12544&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302324
  Stats: 136 lines in 2 files changed: 119 ins; 14 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12544.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12544/head:pull/12544

PR: https://git.openjdk.org/jdk/pull/12544