This fixes a blocker for #11897. `unroll` recursively gets the inner type of any sequence type encountered, so it's inappropriate for codegen that only wants the immediate inner type. However, if a type identifies as a sequence and is nullable, we need to reach through the nullable wrapper first. Gecko does very similar things.
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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#12528 (github issue number if applicable).
- [X] There are tests for these changes
Source-Repo: https://github.com/servo/servo
Source-Revision: 4ae0897175143351439ff5b903d05a79c17e3725
3d7ff72da9