fuzz-testing: Support signature for function meta

[wForget]

What is the problem the feature request solves?

Some function arguments may need to be fixed data type or scalar value, so I propose adding signature to function meta.

Describe the potential solution

I have made an attempt: wForget/fuzz-test-spark-native@5d50fd7

Additional context

No response

[andygrove]

Function signatures with input types and varargs are now defined in fuzz-testing/src/main/scala/org/apache/comet/fuzz/Meta.scala (FunctionSignature / Function), and QueryGen.scala selects compatible columns based on them. Implemented in PR #2614, so closing.