Adds type information to AST nodes synthesized by `Es6RewriteSpreadAn…

…dTest`.

Type information isn't perfect but is sufficient to pass validation checks. It could be tightened later if needed.

This change also updates some tests to add type information to give the validations more to work with.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=197985766

src/com/google/javascript/jscomp/AstValidator.java

@@ -426,7 +426,8 @@ private void validateNameType(Node nameNode) {
   private void validateCallType(Node callNode) {
     // TODO(b/74537281): Shouldn't CALL nodes always have a type, even if it is unknown?
     Node callee = callNode.getFirstChild();
-    JSType calleeTypeI = checkNotNull(callee.getJSType(), callNode);
+    JSType calleeTypeI =
+        checkNotNull(callee.getJSType(), "Callee of\n\n%s\nhas no type.", callNode.toStringTree());
 
     if (calleeTypeI.isFunctionType()) {
       FunctionType calleeFunctionTypeI = calleeTypeI.toMaybeFunctionType();