RFR: 8303702: Provide ThreadFactory to create platform/virtual threads for com/sun/jdi tests [v3]

[Leonid Mesnik]

> Provide a way to start debugee threads as platform or virtual for debugee in com/sun/jdi tests.

Leonid Mesnik has updated the pull request incrementally with one additional commit since the last revision:

  fixed JdbStopThreadidTest to support new change.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12894/files
  - new: https://git.openjdk.org/jdk/pull/12894/files/9951ab3e..0ceb7bc8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12894&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12894&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12894.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12894/head:pull/12894

PR: https://git.openjdk.org/jdk/pull/12894