8176841: Additional Unicode Language-Tag Extensions

8189134: New system properties for the default Locale extensions
8190918: Retrieve the region specific data regardless of language in locale
8191349: Add a new method in j.t.f.DateTimeFormatter to reflect Unicode extensions

Reviewed-by: scolebourne, lancea, rriggs, rgoel, nishjain

src/java.base/share/classes/java/time/format/DecimalStyle.java

@@ -147,6 +147,11 @@ public final class DecimalStyle {
      * Obtains the DecimalStyle for the specified locale.
      * <p>
      * This method provides access to locale sensitive decimal style symbols.
+     * If the locale contains "nu" (Numbering System) and/or "rg"
+     * (Region Override) <a href="../../util/Locale.html#def_locale_extension">
+     * Unicode extensions</a>, returned instance will reflect the values specified with
+     * those extensions. If both "nu" and "rg" are specified, the value from
+     * the "nu" extension supersedes the implicit one from the "rg" extension.
      *
      * @param locale  the locale, not null
      * @return the decimal style, not null