RFR: 7902649: Allow a testsuite to define several TestFilters specific for this suite

[Dmitry Bessonov]

Currently TestSuite class has a method to override that returns only one test filter:

TestFilter createTestFilter(TestEnvironment)

There are situations when test suite has several test filters that it is forced however to hide behind an umbrella
filter. It is more natural and convenient to let test suite return a collection of atomized filters that would be
iterated on the JTHarness side and listed in the test run stats separately and informatively.

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Commit messages:
 - 7902649: Allow a testsuite to define several TestFilters specific for this suite

Changes: https://git.openjdk.java.net/jtharness/pull/2/files
 Webrev: https://webrevs.openjdk.java.net/jtharness/2/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902649
  Stats: 93 lines in 6 files changed: 50 ins; 11 del; 32 mod
  Patch: https://git.openjdk.java.net/jtharness/pull/2.diff
  Fetch: git fetch https://git.openjdk.java.net/jtharness pull/2/head:pull/2

PR: https://git.openjdk.java.net/jtharness/pull/2