[C++] Add arrow::compute::Expression::Equals option that does not compare kernels

[westonpace]

Describe the enhancement requested

This would allow an unbound expression to be considered equal to a bound expression as long as they represent the same call (e.g. same number of arguments, same function name, etc.)

When binding we also do some slight massaging of types (e.g. add(foo_i8, 7_i64) converts to add(foo_i8, 7_i8)). This method should not try and correct for that (e.g. those two example expressions would still be considered unequal). It should mainly just avoid looking at the Call::kernel field and the field reference types and function types.

Once this is added we should enhance the test_expression_serialization test in test_compute.py to use Expression::Equals instead of comparing the string representation of expressions.

Component(s)

C++