RFR: JDK-8261976: Normalize id's used by the standard doclet

[Jonathan Gibbons]

This is a conceptually simple change to ensure that all "id"s generated by the standard doclet use `-` to separate the words of the id. The `src/` change is primarily in the recently-new `HtmlIds` class, but there was one oversight in the recent work for `HtmlIds` in `SourceToHTMLConverter`, which is now fixed.

It's notable now that all "static" ids generated by the doclet contain at least one `-`, and so never conflict with the id for any field name, which cannot contain a `-`.

The tests are updated; all tests pass, of course, including the implicit link check that is default on in almost all tests. A full doc check run on a full JDK docs build did not reveal any unexpected problems.   It wasn't clear which tests to nominate with a bug number, and so (somewhat unusually) I have added the bug number to all affected tests.

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Commit messages:
 - JDK-8261976: Normalize id's used by the standard doclet

Changes: https://git.openjdk.java.net/jdk/pull/2635/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2635&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261976
  Stats: 307 lines in 33 files changed: 1 ins; 1 del; 305 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2635.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2635/head:pull/2635

PR: https://git.openjdk.java.net/jdk/pull/2635