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

[Mikael Vidstedt]

On Wed, 21 May 2025 13:53:37 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> 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

Marked as reviewed by mikael (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25274#pullrequestreview-2858888804