Auto merge of #21647 - AgustinCB:fix-space-leak-when-pipeline-is-closed, r=asajeffrey
Auto merge of #21647 - AgustinCB:fix-space-leak-when-pipeline-is-closed, r=asajeffrey

Fix space leak when pipeline is closed

Add a new control message to drop remove worklets.

Implement `Drop` for `Worklet` and get the worklet thread pool. Use that
pool to send `ExitWorklet` to all the threads with the id of the
`Worklet` that it's dropping.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #17442
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because I don't know how to add a test for this :(

If you consider this needs a test, could you point me out on how to write (and run!) one in this project? I gave this a couple tries, but I wasn't very successful.

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