<i18n dev> RFR: 8310631: test/jdk/sun/nio/cs/TestCharsetMapping.java is spuriously passing [v2]

[Naoto Sato]

> Fixed the failing (well, false-positive) test case. Made the following changes to the test:
> 
> - Corrected the path to the mapping files directory
> - Made sure to fail if the directory path is incorrect
> - Took care of `GB18030` alias, which is dynamically derived at runtime
> - Provided `MS950_HKSCS.map`, which is simply a copy of `HKSCS2008.map`
> - Excluded other failing tests for IBM charsets that do not have map files.

Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:

  Included the failed directory location in the exception message

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15807/files
  - new: https://git.openjdk.org/jdk/pull/15807/files/e2731ff8..6d28a5ae

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15807&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15807&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15807.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15807/head:pull/15807

PR: https://git.openjdk.org/jdk/pull/15807