RFR: JDK-8305620: Missing `break` in DocCommentParser `inlineWord()`

[Jonathan Gibbons]

Please review a fix for the `depth` counting in `DocCommentParser` `inlineWord`.
There was a missing break that caused the count to go high, and because of that the code for the down count needed to be adjusted as well.

The test is modified to be stylistically more like the others with `abc` and `def` surrounding the `{@index...}` tag.  This looks like it may have been a typo, and helped hide the counting issue.

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Commit messages:
 - JDK-8305620: Missing `break` in DocCommentParser `inlineWord()`

Changes: https://git.openjdk.org/jdk/pull/13343/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13343&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305620
  Stats: 8 lines in 2 files changed: 3 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/13343.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13343/head:pull/13343

PR: https://git.openjdk.org/jdk/pull/13343