Finish extern crates grammar

xtask/src/ast_src.rs

@@ -98,7 +98,7 @@ pub(crate) const KINDS_SRC: KindsSrc = KindsSrc {
         "ENUM_DEF",
         "FN_DEF",
         "RET_TYPE",
-        "EXTERN_CRATE_ITEM",
+        "EXTERN_CRATE",
         "MODULE",
         "USE_ITEM",
         "STATIC_DEF",

xtask/src/codegen/rust.ungram

@@ -7,7 +7,7 @@ Item =
   ConstDef
 | EnumDef
 | ExternBlock
-| ExternCrateItem
+| ExternCrate
 | FnDef
 | ImplDef
 | MacroCall
@@ -26,6 +26,9 @@ Module =
 ItemList =
   '{' Attr* Item* '}'
 
+ExternCrate =
+  Attr* Visibility? 'extern' 'crate' (NameRef | 'self') Rename? ';'
+
 FnDef =
  Attr* Visibility? Abi? 'const' 'default' 'async' 'unsafe' 'fn' Name TypeParamList?
  ParamList RetType?
@@ -404,9 +407,6 @@ UseTreeList =
 Rename =
   'as' Name
 
-ExternCrateItem =
-  Attr* Visibility? 'extern' 'crate' (NameRef | 'self') Rename? ';'
-
 Path =
   (qualifier:Path '::')? segment:PathSegment