RFR: 8357173: Split jtreg test group jdk tier3 [v2]

[Erik Joelsson]

> We need to be able to run the jdk_jpackage tests separately from the rest of jdk tier3. To achieve this we would like to introduce tier3_part1 and tier3_part2 groups similar to how lower tiers are split.

Erik Joelsson has updated the pull request incrementally with two additional commits since the last revision:

 - grammar
 - Clarified the group split with comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25274/files
  - new: https://git.openjdk.org/jdk/pull/25274/files/c12c5780..dc18705a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25274&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25274&range=00-01

  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25274.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25274/head:pull/25274

PR: https://git.openjdk.org/jdk/pull/25274