[FEA] Add AST for safe upcasts

[revans2]

Is your feature request related to a problem? Please describe.
Recently I was playing around with #9635 and hit a situation where an int was auto upcast to a long. This was enough to make the join fall back to the CPU. This is a little frustrating when casting an int to a long should be totally safe and supported by AST already.

https://github.com/rapidsai/cudf/blob/70c4283dbd6700bba43440e07b293b2294ea6634/java/src/main/java/ai/rapids/cudf/ast/UnaryOperator.java#L50-L52

Describe the solution you'd like
I would like to see us have the ability to support safe casts from byte, short, and int to INT64 as this should always be safe. I would also love to see us casting from float32 to a float64 as that too should be safe.