grpcquick: give each grpc client test its own QML module URI

The grpc client autotests (bidistream, clientstream, serverstream,
unarycall) register their QML test module under the shared URI
"QmlTestUri", the same name the protobufqml tests used.

Sharing the URI is harmless while each test runs on its own. OpenHarmony
instead deploys all autotests in a single bundle, and we plan to deploy
their QML modules into one shared import directory. Modules that share a
URI would then map to the same path and collide.

Give each test its own URI, GrpcQuickTest.Client.<Test>, and update the
matching QML imports. The generated qtgrpc.tests module these tests also
import is made unique in a follow-up commit.

Task-number: QTBUG-147585
Pick-to: 6.12
Change-Id: I336ff859f27b00d531dd1c48e7b1f250b7a8e775
Reviewed-by: Dennis Oberst <dennis.oberst@qt.io>