RFR: 8366517: DateFormatSymbols(Locale) throws NPE if Locale argument is null

[Naoto Sato]

Adding a `@throws` clause for NPE in `java.text.DateFormatSymbols(Locale)` constructor. The bug suggests it should  throw a `MissingResourceException`, but I don't think we can change this long standing behavior. Instead, explicitly specify the NPE in the javadoc.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/27060/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27060&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366517
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27060.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27060/head:pull/27060

PR: https://git.openjdk.org/jdk/pull/27060