RFR: 7904071: JTReg should report stats of test collections [v3]

[Christian Stein]

> Please review this change accumulating the count numbers of TestNG's and JUnit's text report files and prints them after a test run as follows:
> 
>> `Framework-based tests: 188 = 104 TestNG + 84 JUnit`
> 
> Note that an internal, yet public, API of `SummaryReporter` was changed to be package-private now.

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  Replace stream-based sum computation with inlined accumulation

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Changes:
  - all: https://git.openjdk.org/jtreg/pull/283/files
  - new: https://git.openjdk.org/jtreg/pull/283/files/e75dd7c8..70c653ff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=283&range=02
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=283&range=01-02

  Stats: 12 lines in 1 file changed: 6 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jtreg/pull/283.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/283/head:pull/283

PR: https://git.openjdk.org/jtreg/pull/283