RFR: CODETOOLS-7903317: Fix code to compile extra property definitions

[Jonathan Gibbons]

Please review a fairly simple update to eliminate false positives in comments when looking for the name of the class in a Java source file.

The fix addresses a performance issue when running tests, because the "extra property definition" files were compiled every time jtreg was run, instead of as needed, which is the intent.

The fix is to ignore comments in the source code. The code to do this is copied from equivalent functionality in the langtools `ToolBox` class, which has been in use for many years.

The existing tests for "extra property definition" files have been extended with a test case to ensure that the false positives no longer occur and that the files are not recompiled unnecessarily.

Minor style issues in the main source file have also been fixed.

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Commit messages:
 - Merge with upstream/master
 - CODETOOLS-7903317: Fix code to compile extra property definitions

Changes: https://git.openjdk.org/jtreg/pull/122/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=122&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903317
  Stats: 100 lines in 5 files changed: 96 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jtreg/pull/122.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/122/head:pull/122

PR: https://git.openjdk.org/jtreg/pull/122