Enable feature(doc_cfg) in all lib.rs to prepare for next gir
Gir recently learned to generate doc(cfg())
on all kinds of items so that the documentation neatly shows feature requirements. This is still experimental and requires feature(doc_cfg)
to be enabled. While gir
applies this on autogenerated lib.rs
in sys
crates it does not apply to autogenerated files in the high-level crates, these have been added manually in this MR.