RFR: 8373186: Improve readability of core reflection toString specifications

[Joe Darcy]

Partial implementation of a spec refactoring to get some feedback before writing similar changes for other core reflection types.

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Commit messages:
 - JDK-8373186: Improve readability of core reflection toString specifications

Changes: https://git.openjdk.org/jdk/pull/28688/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28688&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373186
  Stats: 33 lines in 1 file changed: 9 ins; 6 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/28688.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28688/head:pull/28688

PR: https://git.openjdk.org/jdk/pull/28688