grpc-proxy: Add dynamic floating window movement

grpc-proxy: Add dynamic floating window movement

This adds basic movement for floating type of windows. The window needs
to be a floating type for this request to work out.

For the agl-shell protocol, this adds a set_app_float() request while
for gRPC it adds a SetAppPosition() request.

Bug-AGL: SPEC-4863
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: I5ecc4257c3e84d15a8cabb183757753be37867f5