Aggregate all child openjdk test build junit results

In openjdk test build, we display junit results: https://openj9-jenkins.osuosl.org/job/Test_openjdk21_j9_sanity.openjdk_aarch64_mac_Nightly_testList_1/40/testReport/


In the parent build, we only collect TAP files from child builds. It would be great if we also display the junit result at the parent build level. https://openj9-jenkins.osuosl.org/job/Test_openjdk21_j9_sanity.openjdk_aarch64_mac_Nightly/46/

Start with the linked child and parent OpenJ9 Jenkins build pages to compare the existing JUnit and TAP results. Trace how the parent build collects child TAP files, then determine where JUnit results should be aggregated; done means the parent build displays the JUnit results from all child builds.

Written by the indexing model from the issue text.