feat: support Substrait ExtendedExpression

[danepitkin]

It would be neat if we could create Substrait expressions from Ibis expressions. One use case would be to project/filter pyarrow datasets. See https://gist.github.com/ianmcook/f70fc185d29ae97bdf85ffe0378c68e0 for an example that could benefit from this feature.

[gforsyth]

Definitely seems doable -- I think we have all of the appropriate rules in the compiler.
Probably we would want to be able to specify whether we were compiling to a plan or ExtendedExpression when instantiating SubstraitCompiler.

Also, a collection of example ExtendedExpressions and the corresponding ibis code that we think would generate them would go a long ways towards getting this off the ground.