RFR: 8303702: Provide ThreadFactory to create platform/virtual threads for com/sun/jdi tests [v2]

[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:

  more threads are virtualized.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12894/files
  - new: https://git.openjdk.org/jdk/pull/12894/files/60b793be..9951ab3e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12894&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12894&range=00-01

  Stats: 63 lines in 10 files changed: 3 ins; 19 del; 41 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