Merge #4234

4234: Support local_inner_macros r=jonas-schievink a=edwin0cheng

This PR implements `#[macro_export(local_inner_macros)]` support. 

Note that the rustc implementation is quite [hacky][1] too. :)

[1]: 614f273e93/src/librustc_resolve/macros.rs (L456)

Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>

crates/ra_syntax/src/ast/extensions.rs

@@ -423,6 +423,10 @@ impl ast::MacroCall {
             None
         }
     }
+
+    pub fn is_bang(&self) -> bool {
+        self.is_macro_rules().is_none()
+    }
 }
 
 impl ast::LifetimeParam {