grpcquick: use unique QML URIs for generated client modules

The grpc client autotests (bidistream, clientstream, serverstream,
unarycall) generate their protobuf and gRPC types into a QML module via
qt_add_protobuf(... QML QML_URI). All four use the same URI,
"qtgrpc.tests".

This is harmless while each test runs from its own build directory or
separate package. OpenHarmony instead deploys all autotests in a single
bundle, and we plan to deploy their generated QML modules into one
shared import directory. The four modules would then map to the same
path and overwrite one another's qmldir, so at most one test's types
would survive and the others would fail to load their QML.

Give each test its own generated URI, qtgrpc.tests.<test>, matching the
per-test scheme already used by the protobufqml generated modules
(qtprotobufnamespace.tests.<test>), and update the QML imports,
including the inline import in unarycall's createQmlObject() call.

Task-number: QTBUG-147585
Pick-to: 6.12
Change-Id: I3c0b2a6d0e38484d47ec44f86ffea8cdcc9cc036
Reviewed-by: Dennis Oberst <dennis.oberst@qt.io>