7297: Propose trait associated items and autoimport traits on completion r=matklad a=SomeoneToIgnore  Closes #7248 7338: Parse `impl const Trait` r=Veykril a=Veykril Closes #7313 bors r+ Co-authored-by: Kirill Bulatov <mail4score@gmail.com> Co-authored-by: Lukas Wirth <lukastw97@gmail.com>