RFR: JDK-8301201: Allow \n@ inside inline tags using inlineContent [v2]

[Jonathan Gibbons]

> Please review a simple change to allow the use of _newline_ _whitespace_ `@` inside inline tags that allow rich content (that is, those parsed with `inlineContent`) as compared to those that only allow plain text (that is, those parsed with `inlineText`).
> 
> The fix is to delete the code which recognizes `@` as the beginning of a block tag. Compare to the similar fix in [JDK-8241780](https://bugs.openjdk.org/browse/JDK-8241780)
> 
> The general `TagTest.java` is updated for the new feature.

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

  fix broken tests

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12264/files
  - new: https://git.openjdk.org/jdk/pull/12264/files/a27b09b1..6b22d92f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12264&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12264&range=00-01

  Stats: 31 lines in 2 files changed: 17 ins; 3 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/12264.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12264/head:pull/12264

PR: https://git.openjdk.org/jdk/pull/12264