Auto merge of #26756 - servo:write_item, r=jdm
Auto merge of #26756 - servo:write_item, r=jdm

Move most of `SequenceWriter::write_item` to non-generic functions

The size of LLVM IR for the `style` crate is reduced by ~1.5% (27k lines out of 1.8M)

CC https://github.com/servo/servo/issues/26713

KiChjang/servo,splav/servo,splav/servo,splav/servo,KiChjang/servo,KiChjang/servo,splav/servo,splav/servo,KiChjang/servo,KiChjang/servo,KiChjang/servo,splav/servo,KiChjang/servo,splav/servo,KiChjang/servo,splav/servo,splav/servo,KiChjang/servo,splav/servo,KiChjang/servo