[Unity][Transform] Handle symbolic variables in LambdaLift

Prior to this commit, symbolic variables used by a lambda function
would be duplicated between the caller and the lifted-out function.
In addition, shape inference within the lifted-out function was
performed without access to the symbolic variables, resulting in
unnecessary fallback from `R.Tensor([m, n])` to `R.Tensor(ndim=2)`.

This commit updates the `LambdaLift` transform to handle symbolic
variables.  All symbolic variables have unique definitions across the
resulting `IRModule`, and shape inference in the lifted-out function
is aware of symbolic variables that have been exposed to it.