RFR: 8273157: Add convenience methods to Messager

[Joe Darcy]

Hello,

Please review the addition of a half dozen convenience methods to Messager to allow code like

    m.printError("Error message")

rather than

    m.printMessage(Kind.ERROR, "Error message")

For each of notes, warnings, and errors, two methods are added: one taking a message, the second taking a message and an element. There are other overloads of the printMessage method with additional arguments, but they are less commonly used and weren't judged to merit dedicated convenience methods.

The changeset also refactors ~125 of ~150 call sites of printMessage in the langtools regression tests to use the new methods. The updated tests (or tests using the updated files) all pass. I became more convinced of the utility of the new methods after using them in the refactoring.

I'll run a script to update the copyright years before any integration.

CSR for review: https://bugs.openjdk.java.net/browse/JDK-8273160

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Commit messages:
 - 8273157

Changes: https://git.openjdk.java.net/jdk/pull/5309/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5309&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273157
  Stats: 297 lines in 85 files changed: 88 ins; 30 del; 179 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5309.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5309/head:pull/5309

PR: https://git.openjdk.java.net/jdk/pull/5309