RFR: 8361713: JavaFX API docs overview is missing an intro section

[Kevin Rushforth]

This PR adds an introductory section to the JavaFX API docs similar to that of the JDK docs.

Compare the [JavaFX 24 API docs](https://download.java.net/java/GA/javafx24/docs/api/index.html) with the [JDK 24 API docs](https://docs.oracle.com/en/java/javase/24/docs/api/index.html).

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Commit messages:
 - Use custom gradle task to fix dependency issue
 - 8361713: JavaFX API docs overview is missing an intro section

Changes: https://git.openjdk.org/jfx/pull/1842/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1842&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361713
  Stats: 39 lines in 2 files changed: 38 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1842.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1842/head:pull/1842

PR: https://git.openjdk.org/jfx/pull/1842