RFR: JDK-8309150: Need to escape " inside attribute values

[Jonathan Gibbons]

Please review a trivial PR to escape `"` as `"` when writing HTML attribute values enclosed in `"`.

A simple test is added, using a `@spec` tag to introduce a user-defined `id`.

The inverse transformation (from `"` to `"`) needs to be done in the `HtmlParser` for the `JavadocTester` framework.

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Commit messages:
 - JDK-8309150: Need to escape " inside attribute values

Changes: https://git.openjdk.org/jdk/pull/14234/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14234&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309150
  Stats: 78 lines in 3 files changed: 76 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14234.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14234/head:pull/14234

PR: https://git.openjdk.org/jdk/pull/14234