Create an injectable LockHandler

We create an injectable LockHandler that just calls the static
Lock.executeWithLocks function.

I'm not sure what's the correct place to put the LockHandler. I think
model/server is only appropriate for the actual datastore lock. This is a "per request" lock, so maybe request/lock?

-----------------------------

This is the initial step in adding the "lock implicitly released on request death" feature, but it's also useful on its own - easier to test Actions when we can use a fake lock.

To keep this CL simple, we keep using the old Lock as is in most places. We just choose a single example to convert to LockHandler to showcase it. Converting all other uses will be in a subsequent CL.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=167357564

java/google/registry/request/RequestModule.java

@@ -27,6 +27,8 @@ import dagger.Provides;
 import google.registry.request.HttpException.BadRequestException;
 import google.registry.request.HttpException.UnsupportedMediaTypeException;
 import google.registry.request.auth.AuthResult;
+import google.registry.request.lock.LockHandler;
+import google.registry.request.lock.LockHandlerPassthrough;
 import java.io.IOException;
 import java.util.Map;
 import javax.servlet.http.HttpServletRequest;
@@ -122,6 +124,11 @@ public final class RequestModule {
     }
   }
 
+  @Provides
+  static LockHandler provideLockHandler(LockHandlerPassthrough lockHandler) {
+    return lockHandler;
+  }
+
   @Provides
   @JsonPayload
   @SuppressWarnings("unchecked")