Support [] default value for sequences

[jdm]

Adding void passOptionalSequenceWithDefault(optional sequence<long> seq = []); or dictionary Foo { sequence<DOMString> = []; }; yields TypeError: Can't handle non-null default value here.

[tigercosmos]

@jdm could you explain more?

[jdm]

If we add void passOptionalSequenceWithDefault(optional sequence<long> seq = []); to components/script/dom/webidls/TestBinding.webidl, we get a TypeError when executing CodegenRust.py, and it comes from https://dxr.mozilla.org/servo/rev/edb2db55b7fd72370a90fc65c5984d6b7e0f792f/components/script/dom/bindings/codegen/CodegenRust.py#674.

[KiChjang]

@tigercosmos Are you interested in working on this?

[tigercosmos]

Not now. Please take it.

[saschanaz]

Fixed by #22084