RFR: JDK-8322878: Including sealing information Class.toGenericString()

[Joe Darcy]

As recently discussed on core libs, sealed-ness information could be included in the Class.toGenericString() output, analagous to how "modifiers" that also correspond to JVM access flags are handled.

This is the initial spec, implementation, and test updated needed for that change. If there is consensus this is a reasonable direction, I'll create the CSR, etc.

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Commit messages:
 - JDK-8322878: Including sealing information Class.toGenericString()

Changes: https://git.openjdk.org/jdk/pull/17239/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17239&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322878
  Stats: 25 lines in 2 files changed: 16 ins; 1 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/17239.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17239/head:pull/17239

PR: https://git.openjdk.org/jdk/pull/17239