Coercible signature: how to specify some inputs should have exact same type?

[Jefffrey]

Is your feature request related to a problem or challenge?

Looking at btrim for example:

datafusion/datafusion/functions/src/string/btrim.rs

Lines 82 to 93 in f27e50c

	signature: Signature::one_of(
	vec![
	TypeSignature::Coercible(vec![
	Coercion::new_exact(TypeSignatureClass::Native(logical_string())),
	Coercion::new_exact(TypeSignatureClass::Native(logical_string())),
	]),
	TypeSignature::Coercible(vec![Coercion::new_exact(
	TypeSignatureClass::Native(logical_string()),
	)]),
	],
	Volatility::Immutable,
	),

It specifies it accepts 2 string input types. However the planner doesn't coerce them to a common type, leaving it up to the UDF to handle casting to a common type for simplicity (otherwise get explosion of string types to handle):

datafusion/datafusion/functions/src/string/btrim.rs

Lines 32 to 43 in f27e50c

	/// Returns the longest string with leading and trailing characters removed. If the characters are not specified, spaces are removed.
	/// btrim('xyxtrimyyx', 'xyz') = 'trim'
	fn btrim<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
	let use_string_view = args[0].data_type() == &DataType::Utf8View;
	let args = if args.len() > 1 {
	let arg1 = arrow::compute::kernels::cast::cast(&args[1], args[0].data_type())?;
	vec![Arc::clone(&args[0]), arg1]
	} else {
	args.to_owned()
	};
	general_trim::<T, TrimBoth>(&args, use_string_view)
	}

Describe the solution you'd like

Some way in the coercible signature API to specify when inputs should have same type. We previously could do this via:

TypeSignature::Uniform(2, vec![Utf8, Utf8View, LargeUtf8])
TypeSignature::Exact(vec![Utf8, Utf8]) // and other variants
TypeSignature::String(2)

So if we want to still try move toward coercible API, it would be good to support this somehow otherwise its very much less ergonomic for UDFs to handle this logic themselves.

Describe alternatives you've considered

No response

Additional context

No response