RFR: 8294626: Improve URL protocol lower casing [v3]

[Daniel Fuchs]

On Fri, 30 Sep 2022 11:46:39 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Move a simple utility method from `URL` to the shared `sun.net.util.URLUtil` class, rename it for clarity and enhance it so that it returns the string literal if the protocol matches one of the tested variants. This helps reduce dependencies from bootstrap code on `Locale` while improving the performance and allocation pressure in certain applications.
>
> Claes Redestad has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Cleanups
>  - Revert accidental import mangling

LGTM now.

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Marked as reviewed by dfuchs (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10506