RFR: 8267587: Update java.util to use enhanced switch

[Tagir F.Valeev]

On Mon, 24 May 2021 13:44:36 GMT, Daniel Fuchs <dfuchs at openjdk.org> wrote:

>> Inspired by PR#4088. Most of the changes are done automatically using IntelliJ IDEA refactoring. Some manual adjustments are also performed, including indentations, moving comments, extracting common cast out of switch expression branches, etc.
>> 
>> I also noticed that there are some switches having one branch only in JapaneseImperialCalendar.java. Probably it would be better to replace them with `if` statement?
>
> src/java.base/share/classes/java/util/regex/CharPredicates.java line 217:
> 
>> 215:             case "WORD" -> WORD();
>> 216:             default -> null;
>> 217:         };
> 
> This file has lots of changes which are difficult to review. Maybe it should be split out of this PR.

*sigh* GitHub diff tool is really poor and outdated. Here's how it looks in IntelliJ IDEA diff view:
![image](https://user-images.githubusercontent.com/5114450/119436474-6b455b80-bd46-11eb-8865-8b7f30826a8d.png)

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PR: https://git.openjdk.java.net/jdk/pull/4161