RFR: JDK-8175386: Clarify exception behavior of Types utility methods

[Joe Darcy]

Incremental improvements and clarifications in the specification of Types.

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Commit messages:
 - JDK-8175386: Clarify exception behavior of Types utility methods

Changes: https://git.openjdk.org/jdk/pull/17523/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17523&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8175386
  Stats: 15 lines in 1 file changed: 14 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17523.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17523/head:pull/17523

PR: https://git.openjdk.org/jdk/pull/17523