RFR: JDK-8297802: display of @spec tags should mimic that of @see tags

[Jonathan Gibbons]

Please review a simple change to model the list used to display `@spec` tags on the list used to display `@see` tags.

In both cases, the list uses an inline list if the items are short and do not contain commas, or a bulleted list if they are long or contain commas.

The test is updated for the new output.

For now, new CSS styles are introduced for `spec-list` and `spec-list-long`, duplicating `see-list` and `see-list-long`. We might want to merge these into `tag-list` and `tag-list-long`, or some other suitably-named pair.

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Commit messages:
 - fix trailing whitespace
 - combine see-list and spec-list into tag-list
 - JDK-8297802: display of @spec tags should mimic that of @see tags

Changes: https://git.openjdk.org/jdk/pull/11426/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11426&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297802
  Stats: 147 lines in 23 files changed: 41 ins; 12 del; 94 mod
  Patch: https://git.openjdk.org/jdk/pull/11426.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11426/head:pull/11426

PR: https://git.openjdk.org/jdk/pull/11426