Remove hard-coded function aliasing in ANTLR visitor

[alancai98]

Relevant Issue/Bug

None

Requested Solution/Feature

Currently in the ANTLR parser visitor, we convert function names matching CHARACTER_LENGTH and CHAR_LENGTH to the function name char_length:

partiql-lang-kotlin/partiql-parser/src/main/kotlin/org/partiql/parser/internal/PartiQLParserDefault.kt

Lines 1871 to 1872 in 2879f3a

	GeneratedParser.CHARACTER_LENGTH, GeneratedParser.CHAR_LENGTH ->
	identifierSymbol("char_length", Identifier.CaseSensitivity.INSENSITIVE)

This conversion should not be hard-coded within the ANTLR visitor. Realistically, there should be some alias field within the FnSignature that can specify any name alternatives:

partiql-lang-kotlin/partiql-spi/src/main/kotlin/org/partiql/spi/fn/FnSignature.kt

Lines 24 to 34 in 2879f3a

	public data class FnSignature(
	@JvmField public val name: String,
	@JvmField public val returns: PartiQLValueType,
	@JvmField public val parameters: List<FnParameter>,
	@JvmField public val description: String? = null,
	@JvmField public val isDeterministic: Boolean = true,
	@JvmField public val isNullable: Boolean = true,
	@JvmField public val isNullCall: Boolean = false,
	@JvmField public val isMissable: Boolean = true,
	@JvmField public val isMissingCall: Boolean = true,
	) {

We could follow what Trino does w/ their ScalarFunction definition (i.e. define an alias string array):

https://github.com/trinodb/trino/blob/master/core/trino-spi/src/main/java/io/trino/spi/function/ScalarFunction.java#L32C14-L32C19

With this change, the function resolution would occur at a later stage (rather than during parsing) such as during planning using the specified connector metadata.

Describe Alternatives

1. Leave as it is? <- Can be problematic for future UDFs that may have aliases.
2. Some other way to pass along aliases (e.g. previous way to pass along a map of function names to signatures). <- I think adding an alias field to the existing APIs is less confusing for the end user.

Additional Context

Add any other context about the feature request here.

DoD (Definition of Done)

• Hard-coded mapping of function names in ANTLR visitor is removed

[alancai98]

Also applicable to aggregation functions (e.g. SOME and ANY): https://ronsavage.github.io/SQL/sql-99.bnf.html#some