RFR: JDK-8323839: Expand use of Messager convenience methods in langtools regression tests

[Joe Darcy]

Simple refactoring. Remaining uses of "printMessage" are against Trees (where there are no corresponding convenience methods) or for calls to printMessage where there is not an appropriate convenience method overload, etc.

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Commit messages:
 - JDK-8323839: Expand use of Messager convenience methods in langtools regression tests

Changes: https://git.openjdk.org/jdk/pull/17454/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17454&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323839
  Stats: 9 lines in 5 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/17454.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17454/head:pull/17454

PR: https://git.openjdk.org/jdk/pull/17454