RFR: 8191995: Regression: DatePicker must commit on focusLost

[Marius Hanl]

This PR fixes an issue where the `DatePicker` is not committing his value when the focus is lost. 
As the ticket also mentions, this is a regression which last worked on JavaFX 8 and got broken by the refactoring: [JDK-8150946](https://bugs.openjdk.java.net/browse/JDK-8150946)

The fix is to provide the same api  to the `DatePicker` which was introduced by [JDK-8150946](https://bugs.openjdk.java.net/browse/JDK-8150946) for `ComboBox` and `Spinner`.

Note: While fixing this I found a possible bug which I tracked here: [JDK-8277756](https://bugs.openjdk.java.net/browse/JDK-8277756)
-> When creating a `DatePicker` with the second constructor (with `LocalDate` as parameter) two listener won't be added since they are only added at the first constructor (That's also why I added the focusProperty listener in the second constructor).

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Commit messages:
 - 8191995: Regression: DatePicker must commit on focusLost

Changes: https://git.openjdk.java.net/jfx/pull/679/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=679&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8191995
  Stats: 133 lines in 2 files changed: 133 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/679.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/679/head:pull/679

PR: https://git.openjdk.java.net/jfx/pull/679