[Parser] Allow parsing 'any' in structural position within enum associated

value types.

This change simply calls into Parser::startsParameterName, which already
supports parsing 'any' and 'some', instead of repeating the code without
checking for contextual keywords.

Author: hborla

lib/Parse/ParseType.cpp

@@ -1643,8 +1643,7 @@ bool Parser::canParseTypeTupleBody() {
 
       // If the tuple element starts with "ident :", then it is followed
       // by a type annotation.
-      if (Tok.canBeArgumentLabel() && 
-          (peekToken().is(tok::colon) || peekToken().canBeArgumentLabel())) {
+      if (startsParameterName(/*isClosure=*/false)) {
         consumeToken();
         if (Tok.canBeArgumentLabel()) {
           consumeToken();

test/type/explicit_existential.swift

@@ -320,3 +320,12 @@ func testNestedMetatype() {
   let _: (any (P.Type)).Type = (any P.Type).self
   let _: ((any (P.Type))).Type = (any P.Type).self
 }
+
+func testEnumAssociatedValue() {
+  enum E {
+    case c1((any HasAssoc) -> Void)
+    // expected-error@+1 {{use of protocol 'HasAssoc' as a type must be written 'any HasAssoc'}}
+    case c2((HasAssoc) -> Void)
+    case c3((P) -> Void)
+  }
+}