ICU-22314 Refactor GH CI jobs into workflows triggered by modified paths

[echeran]

Testing PRs in personal fork:

• docs only change
• ICU4C only change
• ICU4J only change

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22314
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[mihnita]

LGTM, Thank you!

[mihnita]

Hmm, I wonder if there is something to cover the "transition" between icu4c and icu4j.
When we generate binary resources (.res & co) from C to Java, there are new files in icu4j, so that's OK.
But do we test the stuff in /tools (the root one, not icu4j/tools)
It looks like we don't test that now (before this PR)

(the LGTM / approve still stands, as this is something we don't do today)

[markusicu]

lgtm except for two nits/questions

[jira-pull-request-webhook]

Notice: the branch changed across the force-push!

• .github/workflows/icu_common.yml is different
• .github/workflows/icu_docs.yml is different

View Diff Across Force-Push

~ Your Friendly Jira-GitHub PR Checker Bot