ICU-23333 Create equivalent build.py scripts for all ant tasks

[mihnita]

• Everything was tested on real repos and the results compared against the equivalent ant tasks
• All files were checked with pylint, mypy (type annotations), and formatted with pyink

The code is a very close equivalent of the ant scripts, even if that means it's not very idiomatic Python.
Global variables (a few), each ant task becomes a function, task dependencies means that the function calls the dependent functions first.
We might polish later if desired.

Checklist

• Required: Issue filed: ICU-23333
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
• Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable
• Approver: Feel free to merge on my behalf

[jira-pull-request-webhook]

Notice: the branch changed across the force-push!

• tools/py/libs/py.typed is different

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[mihnita]

A small description on how I "mapped" Ant to Python

Ant has <target>(s), with a name and dependencies, sometime conditions.

I mapped each <target> to a Python def.
I made private def(s) for targets that didn't seem relevant to be called directly from command line (for example <target name="init"> becomes def _init():)

---

For dependencies I had the dependent method call the dependencies:

<target name="cleanprod" depends="init, setup">

becomes:

def cleanprod():
    _init()
    _setup()

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Also, ant invokes the proper target if I pass it in command line:
ant foo will invoke <target name="foo">

For Python I am doing something similar "by hand", by parsing the cli.
So that's the argparse.ArgumentParser piece, with no direct equivalent in the Ant scripts. Each public ex-task (now def) there is a cli option.

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This probably accounts >90% "tricks" in this ant->python conversion.

[echeran]

I didn't take a deep look, but I assume it's fine. Left a few comments where it's worth making a change / easy to make a change, even given that this will be cleaned up again once Ant is fully removed soon.

[markusicu]

mostly optional

[mihnita]

All feedback implemented, thank you.

[jira-pull-request-webhook]

Hooray! The files in the branch are the same across the force-push. 😃

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[jira-pull-request-webhook]

Hooray! The files in the branch are the same across the force-push. 😃

~ Your Friendly Jira-GitHub PR Checker Bot