Rollup merge of #17020 - MaloJaffre:no_transmute, r=nox
Rollup merge of #17020 - MaloJaffre:no_transmute, r=nox

Don't use mem::transmute in from_gecko-weight

Fixes #16966.

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because it's a minor refactor

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