Auto merge of #21126 - gterzian:tasksource_specific_cancelation, r=jdm

Introduce "per task source" cancellation

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #21119 (github issue number if applicable).

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components/script/Cargo.toml

@@ -44,6 +44,7 @@ dom_struct = {path = "../dom_struct"}
 domobject_derive = {path = "../domobject_derive"}
 embedder_traits = {path = "../embedder_traits"}
 encoding_rs = "0.7"
+enum-iterator = "0.2.0"
 euclid = "0.17"
 fnv = "1.0"
 gleam = "0.5"