RFR: JDK-8266044: Nested class summary should show kind of class or interface

[Hannes Wallnöfer]

This is a simple fix to display the actual kind of nested class in the nested class summary table. This is not using `Utils#getTypeElementKindName` since we want to display the signature-like source level kind name (e.g. "enum" rather than "enum class").

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Commit messages:
 - JDK-8266044: Nested class summary should show kind of class or interface

Changes: https://git.openjdk.java.net/jdk/pull/3897/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3897&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266044
  Stats: 11 lines in 2 files changed: 6 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3897.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3897/head:pull/3897

PR: https://git.openjdk.java.net/jdk/pull/3897