xds: Filter Javadoc of "private" classes

The xds package is not at all pretty. There's lots of stuff leaking that
shouldn't. For the moment accept that and just clean up the javadoc.

This is a bit more important now because XdsChannelCredentials and
XdsServerBuilder will be exposed, so users will start noticing stuff
here. Unfortunately this change doesn't fix IDEs auto-suggesting classes
that users shouldn't use.

xds/build.gradle

@@ -81,10 +81,18 @@ jar {
 }
 
 javadoc {
+    exclude 'com/github/udpa/**'
+    exclude 'com/google/security/**'
+    exclude 'io/envoyproxy/**'
+    // Need to clean up the class structure to reduce how much is exposed
+    exclude 'io/grpc/xds/*LoadBalancer*'
+    exclude 'io/grpc/xds/Bootstrapper.java'
+    exclude 'io/grpc/xds/Envoy*'
+    exclude 'io/grpc/xds/XdsAttributes.java'
+    exclude 'io/grpc/xds/XdsClientWrapperForServerSds.java'
+    exclude 'io/grpc/xds/XdsInitializationException.java'
+    exclude 'io/grpc/xds/XdsNameResolverProvider.java'
     exclude 'io/grpc/xds/internal/**'
-    // At the moment there is no public API. Should probably clean up the class structure to reduce
-    // how much is exposed
-    exclude 'io/grpc/xds/**'
 }
 
 shadowJar {