RFR: 8345261: Refactor the Dimension2D classes

[Nir Lisker]

A small refactoring of the Dimension classes.

* `com.sun.javafx.geom.Dimension` was removed and its uses were replaced by `com.sun.javafx.geom.Dimension2D`.
* `com.sun.javafx.geom.Dimension2D` became a record.
* `javafx.geometry.Dimension2D`: fields became `final`.

I'm not sure we need the implementation class at all considering we are free to use the public one.

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Commit messages:
 - Revert static import wildcard use
 - Initial commit

Changes: https://git.openjdk.org/jfx/pull/1653/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1653&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345261
  Stats: 93 lines in 7 files changed: 5 ins; 70 del; 18 mod
  Patch: https://git.openjdk.org/jfx/pull/1653.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1653/head:pull/1653

PR: https://git.openjdk.org/jfx/pull/1653