RFR: 8345136: Update JDK_DOCS property to point to JDK 23 docs [v2]

[Kevin Rushforth]

> Update the docs bundle to point to the JDK 23 docs (we're currently pointing to JDK 21).
> 
> I will need to also download and host a zip bundle and add its checksum to gradle/verification-metadata.xml to avoid breaking our internal CI build.
> 
> As mentioned in [JDK-8325873](https://bugs.openjdk.org/browse/JDK-8325873) when we updated the docs to use JDK 21, we should do this as a part of updating the boot JDK. To facilitate this, and to move more version number properties to a common place, I will create a new `jdk.docs.version` property in `build.properties` and put it near the `jfx.build.jdk.version` property.
> 
> Both the GHA build and our  CI build are successful.

Kevin Rushforth has updated the pull request incrementally with one additional commit since the last revision:

  Move jdk.docs.version before jfx.build.jdk.version

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1663/files
  - new: https://git.openjdk.org/jfx/pull/1663/files/795ed9aa..5a86fde8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1663&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1663&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1663.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1663/head:pull/1663

PR: https://git.openjdk.org/jfx/pull/1663