Auto merge of #29950 - mrobinson:unify-style-crate, r=mukilan

Make Layout 2020/2013 a runtime switch

This change  makes the choice between Layout 2020 and Layout
2013 a runtime switch. The main part of the patch is removing all layout
related compile-time flags from the style crate. This makes the style crate a
lot simpler, but now Layout 2020 parses a good deal of features that it doesn't
support (table, vertical-align, etc). The good news is that we plan to add
these features to Layout 2020.

- Compile a single style for both Layout 2020 and Layout 2013
- Remove layout_2020/layout_2013 features
- Update GitHub workflows for single compilation
- Update test results

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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 #29942
- [x] There are tests for these changes

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