RFR: JDK-8300914: Allow `@` as an escape in documentation comments [v5]

[Jonathan Gibbons]

> Please review a moderately simple update to permit the use of `@` as the escape character in a limited set of escape sequences.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  Improve spec wording

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12372/files
  - new: https://git.openjdk.org/jdk/pull/12372/files/960a48a5..a8097057

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12372&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12372&range=03-04

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12372.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12372/head:pull/12372

PR: https://git.openjdk.org/jdk/pull/12372