RFR: 8296387: [Tooltip, CSS] -fx-show-delay is only applied to the first tooltip that is shown before it is displayed [v12]

[Marius Hanl]

> This PR fixes a long standing issue where the `Tooltip` will always wait one second until it appears the very first time, even if the 
> `-fx-show-delay` was set to another value.
> 
> The culprit is, that the `cssForced` flag is not inside `Tooltip`, but inside the `TooltipBehaviour`. So the very first `Tooltip` gets processed correctly, but after no `Tooltip` will be processed by CSS before showing, resulting in the set `-fx-show-delay` to not be applied immediately.
> 
> Added a bunch of headful and headless tests for the behaviour since there were none before.

Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:

  Change toBase64(..) to add the base64 part as well

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1394/files
  - new: https://git.openjdk.org/jfx/pull/1394/files/84f2faae..26ec665f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1394&range=11
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1394&range=10-11

  Stats: 7 lines in 1 file changed: 0 ins; 3 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1394.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1394/head:pull/1394

PR: https://git.openjdk.org/jfx/pull/1394