RFR: 8297311: Improve exception message thrown by java.net.HostPortrange::toLowerCase(String s) [v2]

[Jaikiran Pai]

> Can I please get a review of this change which proposes to enhance an exception message in `java.net.HostPortrange::toLowerCase`, as requested in https://bugs.openjdk.org/browse/JDK-8297311?
> 
> The commit here includes (only) the character, which was found to be invalid, in the exception message. The character will be printed out in `\uXXXX` format to take into account any unprintable characters.
> 
> A new test has been introduced to verify that the introduction of this change doesn't introduce any regression and does indeed include the expected exception message.

Jaikiran Pai has updated the pull request incrementally with one additional commit since the last revision:

  review comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11407/files
  - new: https://git.openjdk.org/jdk/pull/11407/files/82826ed4..8b9a428d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11407&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11407&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11407.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11407/head:pull/11407

PR: https://git.openjdk.org/jdk/pull/11407