test(cts): Update regions in while_loop tests

Following a change to the serialization library spec, while_loop tests have been updated to ensure each block is in its own region. This also ensures tensors are defined in the block where they are used.

The old format has been disallowed and will now cause the reference model to error.

Signed-off-by: Madeleine Dunn madeleine.dunn@arm.com