Fixes #90125 - Add a task instancePolicy to task runOptions

[alpalla]

Summary

Fixes #90125. Added an instancePolicy to runOptions. The instancePolicy is applied when creating a new instance of a task once the instanceLimit has been reached.
The instancePolicy is as follows:

1. terminateNewest: the newest instance is terminated
2. terminateOldest: the oldest instance is terminated
3. prompt: the QuickPick is shown and the user picks an instance to restart (this is the default option)
4. warn: do nothing (do not terminate an existing instance or create a new one) and show a warning that indicates that the instanceLimit has been reached
5. silent: do nothing

Implementation notes

• any task selected to be "terminated" by the instancePolicy is effectively restarted
• the TerminalTaskSystem getLastInstance() method has been expanded in scope and is now called getNthInstance. As the name suggests it returns the Nth instance of a task given a number. If no index is given, it returns the last instance by default. I used a for loop instead of doing a forEach on Object.keys so that I could exit early once the right instance was found
• when an instance is created, slightly changed the way I previously set its id so as to avoid cases in which an instance of an instance was being created and the id would be appended with |<COUNTER> multiple times

Testing changes

Create a tasks.json and set the instancLimit and instancePolicy properties. Here is an example configuration:

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "echo",
            "type": "shell",
            "command": "sleep 20 && echo Hello",
            "runOptions": {
                "instanceLimit": 2,
                "instancePolicy": "terminateOldest"
            }
        }
    ]
}

Ensure that once the instanceLimit is reached, the chosen instancePolicy behaves as described at the beginning of this PR.

P.S.

I would suggest not having the prompt option as the default option simply because in the default case where instanceLimit == 1, the user would be shown the QuickPick which would contain only one entry since there is only one active instance. Personally, I think it would make more sense to have another instancePolicy option which would ask the user to terminate or restart the last instance. This would maintain the current behavior and use the current terminate/restart notification, while I think being the least confusing option in the case where runOptions is set to all default settings.

[alpalla]

@alexr00 any updates regarding anything I can do to move forward with this PR? 😃

[sky126]

need this feature

[alexr00]

Can you add an enum description for this?

[alexr00]

I haven't had a chance to do a full review yet, but I hope to next week. Can you resolve the conflicts?

[alpalla]

Sure! I'll resolve the conflicts and add that enum description 👍

[alpalla]

@alexr00 I can't resolve the conflicts and test the resulting code locally because it seems like a couple of things are broken in the latest build. The main issues are:

1. the instanceLimit doesn't seem to be respected anymore (meaning I can create K instances of a task with a limit of N where K > N).
2. If I create n instances of a task and let all instances run to completion, it looks like they are not automatically terminated because all instances are still visible as options to terminate.

I can resolve the conflicts via GitHub without testing the resulting code first but I'm a little hesitant to do so. Let me know how I should proceed, thanks!

[onelivesleft]

Is this feature dead in the water? Would be a great addition.

[alexr00]

Closing in favor of the newer one: #117129