Please review this PR which adds the method `caseFoldLanguageTag(String languageTag)` to java.util.Locale.
This method case folds a language tag to adhere to _[section 2.1.1. Formatting of Language Tags of RFC5646](https://www.rfc-editor.org/rfc/rfc5646.html#section-2.1)_. This format is defined as _"All subtags, including extension and private use subtags, use lowercase letters with two exceptions: two-letter and four-letter subtags that neither appear at the start of the tag nor occur after singletons. Such two-letter subtags are all uppercase ... and four-letter subtags are titlecase."_. In order to match the behavior of existing language tag related Locale methods, this method matches the 2.1.1 RFC5646 specification with the following **exceptions**: - Will not case fold variant subtags - Will not case fold private use subtags prefixed by "lvariant" As an example, `caseFoldLanguageTag("JA-JPAN-JP-U-CA-JAPANESE-x-RANDOM-lvariant-JP")` returns _"ja-Jpan-JP-u-ca-japanese-x-random-lvariant-JP"_. Further examples can be seen in the test file. ------------- Commit messages: - Copyright year for LangTag - Space - Add PR example to tests - Add case for grandfathered tag in specification - Consider private use variant prefix (JDK special cases) - Cache the potential legacy tag - Remove leftover comments in LanguageTag - Adjust imports in LanguageTag.java - Add implementation to LanguageTag.java - Add specification to Locale - ... and 1 more: https://git.openjdk.org/jdk/compare/d063b896...25be34d9 Changes: https://git.openjdk.org/jdk/pull/13679/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13679&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8159337 Stats: 251 lines in 3 files changed: 247 ins; 2 del; 2 mod Patch: https://git.openjdk.org/jdk/pull/13679.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/13679/head:pull/13679 PR: https://git.openjdk.org/jdk/pull/13679
