RFR: 8314597: Deprecate for removal protected access methods in converters

[Nir Lisker]

Deprecating for removal `getDateFormat()` in `DateTimeStringConverter` and `DateTimeStringConverter` after it was removed already in `DateTimeStringConverter`, and `getNumberFormat()` in `NumberStringConverter` (and subclasses).

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Commit messages:
 - Deprecate protected methods

Changes: https://git.openjdk.org/jfx/pull/1294/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1294&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314597
  Stats: 27 lines in 6 files changed: 18 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jfx/pull/1294.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1294/head:pull/1294

PR: https://git.openjdk.org/jfx/pull/1294