RFR: 8254964: Fix default values in Spinner class

[Nir Lisker]

Added 2 `@defaultValue` and fixed the incorrect default for `editable`. Also corrected a typo that doesn't show anyway
in the docs.

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

Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jfx/pull/323/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=323&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254964
  Stats: 5 lines in 1 file changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/323.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/323/head:pull/323

PR: https://git.openjdk.java.net/jfx/pull/323