MLBEDSW-7709: MLCE: Crash when rewriting split op

- A crash occurred due to NoneType subscriptable error when
rewriting a Slice op. The reason was that the Size tensor did
not contain any data.

- Added constraint pushing the Slice operator to the CPU if
begin or size tensor are empty.

- Added test to supported operators
- Updated SUPPORTED_OPS.md

Change-Id: Ide204cae24e5871f0e6ae1fdc98ac68d0ce4d3ae
Signed-off-by: Johan Alfven <johan.alfven@arm.com>