RFR: 8343832: Enhance test summary with number of skipped tests [v4]

[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.

Ivan Bereziuk has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Merge branch 'master' into 8343832_enhance_test_summary
 - indented the comment
 - remove resorting zero-ing of $1_SKIPPED as preceding gawk always assigns the value
 - 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:
  - all: https://git.openjdk.org/jdk/pull/22245/files
  - new: https://git.openjdk.org/jdk/pull/22245/files/a2003355..dda4e2fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22245&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22245&range=02-03

  Stats: 146900 lines in 3883 files changed: 100593 ins; 33547 del; 12760 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