Move the infinite loop coercion check to defaultValue validation

Author: benjie

spec/Section 3 -- Type System.md

@@ -818,8 +818,9 @@ of rules must be adhered to by every Object type in a GraphQL schema.
          characters {"__"} (two underscores).
       2. The argument must accept a type where {IsInputType(argumentType)}
          returns {true}.
-      3. If specified, {defaultValue} must be compatible with {argumentType}
-         as per the coercion rules for that type.
+      3. If specified, {defaultValue} must be compatible with {argumentType} as
+         per the coercion rules for that type, and coercion of {defaultValue}
+         must not cause an infinite loop.
 3. An object type may declare that it implements one or more unique interfaces.
 4. An object type must be a super-set of all interfaces it implements:
    1. Let this object type be {objectType}.
@@ -1469,8 +1470,7 @@ is constructed with the following rules:
 
 * If no value is provided for a defined input object field and that field
   definition provides a default value, the result of coercing the default value
-  according to the coercion rules of the input field type should be used (if
-  this coercion would cause an infinite loop, a query error should be thrown).
+  according to the coercion rules of the input field type should be used.
   If no default value is provided and the input object field's type is
   non-null, an error should be thrown. Otherwise, if the field is not required,
   then no entry is added to the coerced unordered map.
@@ -1531,7 +1531,8 @@ Literal Value            | Variables               | Coerced Value
    3. The input field must accept a type where {IsInputType(inputFieldType)}
       returns {true}.
    4. If specified, {defaultValue} must be compatible with {inputFieldType} as
-      per the coercion rules for that type.
+      per the coercion rules for that type, and coercion of {defaultValue} must
+      not cause an infinite loop.
 
 
 ### Input Object Extensions