allow functions with identical signatures in different extensions to coexist

[vbarua]

Currently, substrait-java cannot handle functions with identical signatures, even if they are present in different extensions files.

substrait-java should be updated to allow this, as these are technically not duplicate functions.

See substrait-io/substrait#631 for an example of this issue occuring.

[jacques-n]

Definitely should try to fix this as it's being used as a reason to hold off doing natural things in substrait-io/substrait

[vbarua]

Actually handling this might be a big change, but if we want to introduce the changes that would break this in substrait it's relatively straightforward to add a workaround hack into substrait-java to exclude duplicated definitions. Effectively, when we build the default extension we would have a blocklist of certain extension that we we would ignore.