Auto merge of #24220 - rasviitanen:domstringlist, r=jdm

add webidl bindings for DOMStringList

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To prepare for the implementation of `IndexedDB` a DOM interface for `DOMStringList` is added.

This change:
* Adds a new IDL file for `DOMStringList`
* Lists `domstringlist.rs` in `mod.rs`
* Defines a new DOMStruct `DOMStringList`
* Changes some test expectations related to `DOMStringList`
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #24208

- [X] These changes do not require tests because:
We are not yet able to fully test the functions of `DOMStringList` in the WPT, because it is not possible to create an object of the type `DOMStringList` until e.g. `indexeddb` or `location.ancestorOrigins` is implemented.

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