Add new TYPE_BOUND_LIST and TYPE_BOUND syntax kinds

These are now used when parsing type bounds. In addition parsing paths inside a
bound now does not recursively parse paths, rather they are treated as separate
bounds, separated by +.

crates/ra_syntax/src/grammar.ron

@@ -243,6 +243,8 @@ Grammar(
         "PARAM",
         "SELF_PARAM",
         "ARG_LIST",
+        "TYPE_BOUND",
+        "TYPE_BOUND_LIST",
     ],
     ast: {
         "SourceFile": (
@@ -577,6 +579,17 @@ Grammar(
             traits: ["AttrsOwner"],
         ),
         "Lifetime": ( traits: ["AstToken"] ),
+        "TypeBound": (
+            options: [
+                "TypeRef",
+                "Lifetime",
+            ]
+        ),
+        "TypeBoundList": (
+            collections: [
+                ["bounds", "TypeBound"],
+            ]
+        ),
         "WhereClause": (),
         "ExprStmt": (
             options: [ ["expr", "Expr"] ]