Wr/delete custom labels

[WillieRuemmele]

What does this PR do?

when a single CL is specified for delete, only delete that label from the CLs file

What issues does this PR fix or reference?

@W-13167950@
forcedotcom/cli#2118

[mshanemc]

for every custom label in the CS, this calls STL.deleteCustomLabels on every label in the set.

Some of those are going to be targeted multiple times?

Maybe you want to do that filter of labels once at the top of the method rather than inside the per-component loop

[mshanemc]

QA: turned Willie's STL PR into 3.2.0-beta.1 for local testing

using the sfdx-delete-customlabel repo, sf project deploy start

source delete

✅ can delete one label via sf project delete source --metadata CustomLabel:KeepMe2 --track-source
👎🏻 I don't think this is true now for Labels. I don't expect you to delete the file.

This operation will delete the following files on your computer and in your org:
/Users/shane.mclaughlin/eng/repros/sfdx-delete-customlabel/force-app/main/default/labels/CustomLabels.labels-meta.xml

✅👎🏻 error when deleting something fictitious. Expected our usual red Error: blah stuff, and something about why, maybe?

👎🏻 and did you really update source tracking?

2 labels remain in the file, and I say to delete one of them, and then make up something else to delete.
✅ nothing is deleted.

✅ when I delete both remaining labels, the file disappears

---

project deploy/retrieve stuff

I put the labels back in the org.
✅ delete label in org, looks fine locally after retrieve (pull-like)
✅ when I delete all the labels from the org, the file deletes.

I put the labels back in the local project and the org.
remove 1 label from the local file
❌ project deploy start (like a push)

It gives the output that seems correct, but the label is still in the org

| State     Name         Type         Path                                                       
| ───────── ──────────── ──────────── ────────────────────────────────────────────────────────── 
| Unchanged KeepMe1      CustomLabel  force-app/main/default/labels/CustomLabels.labels-meta.xml 
| Unchanged KeepMe2      CustomLabel  force-app/main/default/labels/CustomLabels.labels-meta.xml 
| Unchanged CustomLabels CustomLabels force-app/main/default/labels/CustomLabels.labels-meta.xml 

If you restore the label locally and deploy again, it notices the change correctly and the re-added label is in the output.

📓 Not tested: multiple directory scenarios

[mshanemc]

QA notes:

retested using https://github.com/forcedotcom/source-tracking/pull/388/files and the corresponding change for PDR.

👍🏻 output messages are good
✅ successfully deleted 1 and multiple labels from local file and verified deletion in org

Note: this set of PRs does not modify the behavior of push so that it stays consistent with source:deploy and underlying metadata api behavior expectations.