Auto merge of #158013 - khyperia:AliasTy-def_id, r=BoxyUwU

remove AliasTy::def_id()



this is part of rust-lang/rust#156181

as well as part of rust-lang/rust#152245

this immediately uses [the recently-introduced `Alias<>` type](rust-lang/rust#156538) to narrow the kinds of aliases allowed in various places in code

fyi @lcnr

r? @BoxyUwU

Author: bors