RFR: JDK-8305591: Cleanup use of `newline` flag in DocCommentParser

[Jonathan Gibbons]

Please remove a simple cleanup fix, to remove unnecessary assignments to set the `newline` flag  to `true` in `DocCommentParser`. The flag is always set appropriately in `nextChar()`.

This removes a number of "fall-through" cases in switch statements. In reviewing the use of `@SuppressWarnings("fall through")` it was noted that there is a missing `break` in `case '@'` in `inlineWord()`. Fixing this breaks a test. This will be addressed separately. [JDK-8305620](https://bugs.openjdk.org/browse/JDK-8305620)

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Commit messages:
 - JDK-8305591: Cleanup use of `newline` flag in DocCommentParser

Changes: https://git.openjdk.org/jdk/pull/13341/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13341&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305591
  Stats: 18 lines in 1 file changed: 0 ins; 18 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13341.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13341/head:pull/13341

PR: https://git.openjdk.org/jdk/pull/13341