[BACKEND] Fix unsupported view op created during optimizations (#2510)

When propagating layout we were generating a view op with mismatching
total number of element per threads. Lowering such op would require
exchanging data across threads.
This change prevents the optimizer from generating such cases. This may
require further optimizations in the future.

include/triton/Dialect/TritonGPU/IR/Dialect.h

@@ -107,6 +107,9 @@ bool isSharedEncoding(Value value);
 
 bool isExpensiveCat(CatOp cat, Attribute targetEncoding);
 
+// Return true if a view between the two types cannot be implemented as a no-op.
+bool isExpensiveView(Type srcType, Type dstType);
+
 } // namespace gpu
 } // namespace triton
 } // namespace mlir