Auto merge of #11827 - servo:geckolib-no-const-fn, r=emilio

Generate geckolib structs with -no-bitfield-methods

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This makes rust-bindgen not generate a bunch of methods that were not used, including `const fn` ones.

This helps with #11815 since `const fn` is unstable.

(Note that running `regen_style_structs.sh` without changing it made a bunch of unrelated changes to `structs_*.rs`, probably because I had a different Gecko version. I first made a commit of that, then added `-no-bitfield-methods`, regenerated, made another commit, then removed the first commit with `git rebase -i master@{u}`.)

r? @emilio

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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 part of #11815 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [x] These changes do not require new tests because they’re only removing dead code.

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