user interface for command input output instead of type (#313)

This will eliminate extra type alias link that users need to
click through when inspecting the operation input/output shape
in the API reference

Author: AllanZhengYP

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/CommandGenerator.java

@@ -192,13 +192,13 @@ private void writeInputType(String typeName, Optional<StructureShape> inputShape
             StructureShape input = inputShape.get();
             List<MemberShape> blobStreamingMembers = getBlobStreamingMembers(input);
             if (blobStreamingMembers.isEmpty()) {
-                writer.write("export type $L = $T;", typeName, symbolProvider.toSymbol(input));
+                writer.write("export interface $L extends $T {}", typeName, symbolProvider.toSymbol(input));
             } else {
                 writeStreamingInputType(typeName, input, blobStreamingMembers.get(0));
             }
         } else {
             // If the input is non-existent, then use an empty object.
-            writer.write("export type $L = {}", typeName);
+            writer.write("export interface $L {}", typeName);
         }
     }
 
@@ -207,10 +207,10 @@ private void writeOutputType(String typeName, Optional<StructureShape> outputSha
         // to a defined output shape.
         writer.addImport("MetadataBearer", "__MetadataBearer", TypeScriptDependency.AWS_SDK_TYPES.packageName);
         if (outputShape.isPresent()) {
-            writer.write("export type $L = $T & __MetadataBearer;",
+            writer.write("export interface $L extends $T, __MetadataBearer {}",
                     typeName, symbolProvider.toSymbol(outputShape.get()));
         } else {
-            writer.write("export type $L = __MetadataBearer", typeName);
+            writer.write("export interface $L extends __MetadataBearer {}", typeName);
         }
     }
 
@@ -235,8 +235,14 @@ private void writeStreamingInputType(String typeName, StructureShape inputShape,
         Symbol inputSymbol = symbolProvider.toSymbol(inputShape);
         String memberName = streamingMember.getMemberName();
         String optionalSuffix = streamingMember.isRequired() ? "" : "?";
-        writer.openBlock("export type $L = Omit<$T, $S> & {", "};", typeName, inputSymbol, memberName, () ->
-            writer.write("$1L$2L: $3T[$1S]|string|Uint8Array|Buffer;", memberName, optionalSuffix, inputSymbol));
+        writer.openBlock("type $LType = Omit<$T, $S> & {", "};", typeName, inputSymbol, memberName, () -> {
+            writer.writeDocs(String.format("For *`%1$s[\"%2$s\"]`*, see {@link %1$s.%2$s}.",
+                    inputSymbol.getName(), memberName));
+            writer.write("$1L$2L: $3T[$1S]|string|Uint8Array|Buffer;", memberName, optionalSuffix, inputSymbol);
+        });
+        writer.writeDocs(String.format("This interface extends from `%1$s` interface. There are more parameters than"
+                + " `%2$s` defined in {@link %1$s}", inputSymbol.getName(), memberName));
+        writer.write("export interface $1L extends $1LType {}", typeName);
     }
 
     private void addCommandSpecificPlugins() {