Auto merge of #23253 - BartGitHub:refactor-promise-compartment, r=jdm

Refactor promise compartment

<!-- Please describe your changes on the following line: -->
This PR adds a mechanism to verify that certain code is executed inside a ```JSAutoCompartment```, and applies this to the ```Promise::new_in_current_compartment``` constructor.

r? @jdm

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #23167

<!-- Either: -->
- [x] These changes do not require tests because they do not change existing functionality.

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/23253)
<!-- Reviewable:end -->

components/script/fetch.rs

@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+use crate::compartments::{AlreadyInCompartment, InCompartment};
 use crate::dom::bindings::codegen::Bindings::RequestBinding::RequestInfo;
 use crate::dom::bindings::codegen::Bindings::RequestBinding::RequestInit;
 use crate::dom::bindings::codegen::Bindings::ResponseBinding::ResponseBinding::ResponseMethods;
@@ -125,7 +126,6 @@ fn request_init_from_request(request: NetTraitsRequest) -> RequestBuilder {
 
 // https://fetch.spec.whatwg.org/#fetch-method
 #[allow(unrooted_must_root)]
-#[allow(unsafe_code)]
 pub fn Fetch(
     global: &GlobalScope,
     input: RequestInfo,
@@ -134,7 +134,8 @@ pub fn Fetch(
     let core_resource_thread = global.core_resource_thread();
 
     // Step 1
-    let promise = unsafe { Promise::new_in_current_compartment(global) };
+    let aic = AlreadyInCompartment::assert(global);
+    let promise = Promise::new_in_current_compartment(global, InCompartment::Already(&aic));
     let response = Response::new(global);
 
     // Step 2