feat: EXPOSED-89 Support functions in Create Index

[bog-walk]

Add support for functional indices.

Problem 1 - Getting Table Info:
Data class Index currently gets Table information from user-provided columns. If an index is defined using only functions, the table property cannot be derived, since Function class does not store such info. In this case, table info needs to be directly provided, so this is done automatically if a user defines functions.

Problem 2 - Naming the Index:
Current behavior is to append column names to table name. Function class does not store a name, so it will be derived from the function string (works for Exposed functions of the form NAME(expr)). If a custom function doesn't have this format, the entire string is used instead.

• Alternative: Force users to provide a customIndexName if functions are included.

Problem 3 - Multiple Vararg Prohibited:
All current index creation functions have a parameter named columns that only accepts List<Column<*>>. Multiple function arguments need to be supported, but a second vararg cannot be used, so the new parameter accepts List<ExpressionWithColumnType<*>> instead.

• Alternative: Change columns type to this mutual super class so the user could easily provide column and function arguments together without named arguments. But then the name columns would be misleading and would need to be replaced with something like columnsAndFunctions or keyFields, which would break uses that include named arguments. This would also break Exposed code that uses Index.columns, which would require handling/filtering to provide expected List<Column<*>>.

Note:

• Add dropIndex() override for Oracle as default was not correct.