Update intEnum generation to use type alias

Due to type definitions requiring strict casting and implementation
overhead in protocol generation, this commit uses type aliases to
generate intEnums as an intermediate step until migrating back to
type definitions.

This change is backwards compatible except for the removed `Values()`
method that was on intEnum type definitions, but not definable on type
aliases since defining methods on base types (`int32`) is not permitted.

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/CodegenUtils.java

@@ -419,6 +419,7 @@ public static boolean isNumber(Shape shape) {
             case BYTE:
             case SHORT:
             case INTEGER:
+            case INT_ENUM:
             case LONG:
             case FLOAT:
             case DOUBLE:

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/IntEnumGenerator.java

@@ -48,7 +48,9 @@ final class IntEnumGenerator implements Runnable {
     public void run() {
         Symbol symbol = symbolProvider.toSymbol(shape);
 
-        writer.write("type $L int32", symbol.getName()).write("");
+        // TODO(smithy): Use type alias instead of type definition until refactoring
+        // protocol generators is prioritized.
+        writer.write("type $L = int32", symbol.getName()).write("");
 
         writer.writeDocs(String.format("Enum values for %s", symbol.getName()));
         Set<String> constants = new LinkedHashSet<>();
@@ -84,6 +86,9 @@ public void run() {
             }
         }).write("");
 
+        // TODO(smithy): type aliases don't allow defining methods on base types (e.g. int32).
+        // Uncomment generating the Value() method when the type alias is migrated to type definition.
+        /*
         writer.writeDocs(String.format("Values returns all known values for %s. Note that this can be expanded in the "
                 + "future, and so it is only as up to date as the client.%n%nThe ordering of this slice is not "
                 + "guaranteed to be stable across updates.", symbol.getName()));
@@ -94,5 +99,6 @@ public void run() {
                 }
             });
         });
+        */
     }
 }

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/ShapeValueGenerator.java

@@ -304,6 +304,7 @@ protected void writeScalarPointerInline(GoWriter writer, MemberShape member, Nod
                 funcName = "Int16";
                 break;
             case INTEGER:
+            case INT_ENUM:
                 funcName = "Int32";
                 break;
             case LONG:
@@ -669,6 +670,7 @@ public Void numberNode(NumberNode node) {
                 case BYTE:
                 case SHORT:
                 case INTEGER:
+                case INT_ENUM:
                 case LONG:
                 case FLOAT:
                 case DOUBLE:

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/integration/HttpBindingProtocolGenerator.java

@@ -767,6 +767,7 @@ private void writeHttpBindingSetter(
                 locationEncoder.accept(writer, "Short(" + operand + ")");
                 break;
             case INTEGER:
+            case INT_ENUM:
                 locationEncoder.accept(writer, "Integer(" + operand + ")");
                 break;
             case LONG:
@@ -1211,6 +1212,7 @@ private String generateHttpHeaderValue(
                 writer.write("if err != nil { return err }");
                 return "int16(vv)";
             case INTEGER:
+            case INT_ENUM:
                 writer.addUseImports(SmithyGoDependency.STRCONV);
                 writer.write("vv, err := strconv.ParseInt($L, 0, 32)", operand);
                 writer.write("if err != nil { return err }");