RFR: 8343832: Enhance test summary with number of skipped tests

[Ivan Bereziuk]

The output for Jtreg v7.5 was [enhanced](https://github.com/openjdk/jtreg/pull/217/files#diff-b6ab77bf651f1fd9a83c3ca0aab9cd24ae5c08cef41e6e257f7eaccc07c7c366R947) with [information about skipped tests](https://github.com/openjdk/jtreg/blob/master/src/share/doc/javatest/regtest/faq.md#what-do-all-those-numbers-in-the-test-results-line-mean).

Use the additional information in the "summary" block printed at the end of `make test` target.

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Commit messages:
 - lowercased Jtreg. fixed typos in the comment
 - aggregated calculation for many categoires of skipped tests into one gawk block with regex
 - 8343832: Enhance test summary with number of skipped tests

Changes: https://git.openjdk.org/jdk/pull/22245/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22245&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343832
  Stats: 40 lines in 1 file changed: 30 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/22245.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22245/head:pull/22245

PR: https://git.openjdk.org/jdk/pull/22245