MLBEDSW-10899: Handle RESCALE with output unsigned properly

Networks with a RESCALE that writes to graph output and has
output_unsigend set lost the unsignedness of the output tensor
when the ReinterpretCast op was handled. This caused wrong OFM
clipping and zero point.

This patch changes the following:

* Don't add REINTERPRETCAST before/after RESCALE. Instead, keep
  the RESCALE and its attributes and deal with the unsigned
  input/output when lowering SchedIR to HLC.
* Reset all buffers when cloning IFM. This is important when
  cloning IFM with the purpose of creating a new intermediate
  tensor. If the IFM is constant, the cloned tensor will inherit
  the contant data as well, which is not desired in most cases.

Signed-off-by: Johan Gunnarsson <johan.gunnarsson@arm.com>
Change-Id: Ie0adbdfbee18e92568acb1d1f44637fbdd309e8d