<i18n dev> RFR: 8336847: Use pattern match switch in NumberFormat classes

[Justin Lu]

As discussed in https://github.com/openjdk/jdk/pull/19513#discussion_r1684957942, there is code within java.text.NumberFormat (and subclasses) that can use the pattern match switch to improve readability.

As this is simply cleanup, there is no regression test added.

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

Commit messages:
 - add null case to restore IAE behavior
 - init

Changes: https://git.openjdk.org/jdk/pull/20302/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20302&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336847
  Stats: 142 lines in 3 files changed: 0 ins; 29 del; 113 mod
  Patch: https://git.openjdk.org/jdk/pull/20302.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20302/head:pull/20302

PR: https://git.openjdk.org/jdk/pull/20302