RFR: JDK-8301810: Bug in doctree DocCommentTester.compress [v2]

[Jonathan Gibbons]

> Please review a minor but long-standing bug in the code to "compress" long strings in the `doctree` `DocCommentTester` class.
> 
> The primary change is in `DocCommentTester`, to fix the code, and make it somewhat more robust.  The change does break some golden output, in comments and files, so advantage is taken to increase the max size of compressed strings.

Jonathan Gibbons has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into 8301810.doctree-doccommenttester-compress
 - JDK-8301810: Bug in doctree DocCommentTester.compress

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/12418/files
  - new: https://git.openjdk.org/jdk/pull/12418/files/0e670849..08b359fa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12418&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12418&range=00-01

  Stats: 3615 lines in 104 files changed: 2292 ins; 887 del; 436 mod
  Patch: https://git.openjdk.org/jdk/pull/12418.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12418/head:pull/12418

PR: https://git.openjdk.org/jdk/pull/12418