Auto merge of #68717 - petrochenkov:stabexpat, r=varkor

Stabilize fn-like proc macros in expression, pattern and statement positions

I.e. all the positions in which stable `macro_rules` macros are supported.

Depends on https://github.com/rust-lang/rust/pull/68716 ("Stabilize `Span::mixed_site`").

cc https://github.com/rust-lang/rust/issues/54727
cc https://github.com/rust-lang/rust/issues/54727#issuecomment-580647446

Stabilization report: https://github.com/rust-lang/rust/pull/68717#issuecomment-623197503.

mini-macro/src/lib.rs

@@ -1,4 +1,4 @@
-#![feature(proc_macro_quote, proc_macro_hygiene)]
+#![feature(proc_macro_quote)]
 #![deny(rust_2018_idioms)]
 // FIXME: Remove this attribute once the weird failure is gone.
 #![allow(unused_extern_crates)]

tests/ui/auxiliary/proc_macro_derive.rs

@@ -1,7 +1,7 @@
 // no-prefer-dynamic
 
 #![crate_type = "proc-macro"]
-#![feature(repr128, proc_macro_hygiene, proc_macro_quote)]
+#![feature(repr128, proc_macro_quote)]
 
 extern crate proc_macro;
 

tests/ui/crashes/ice-3741.rs

@@ -1,7 +1,6 @@
 // aux-build:proc_macro_crash.rs
 // run-pass
 
-#![feature(proc_macro_hygiene)]
 #![warn(clippy::suspicious_else_formatting)]
 
 extern crate proc_macro_crash;