This PR moves the core_functions to a separate extension, instead of sitting inline in the main source tree. The core_functions library is statically shipped with (almost) all clients, similar to how the parquet client is shipped. The main idea here is that for the WASM build we can leave out the core_functions of the main binary distribution - and load it only later when one of the functions is referenced. This decreases the size of the initial WASM payload.

For testing purposes, the core_functions extension is always loaded currently, as many tests rely on core functions being present and adding the correct requires and fixing all of the C++ tests is a lot of work. This should be done at some point - in particular to test the auto-loading fully.

Moving Functions To Main

As part of this PR, we must make sure that there are no references to core_functions from within the main library. This PR accomplishes that by moving a number of functions out of core_functions and into the main library. At some point we should revisit this - as likely several functions can be moved back out of the main library and into core_functions with more careful planning.

Auto-Loading Function Overloads

One side-effect of moving core_functions to a separate extension is that there are now functions that are defined in multiple extensions. For example, the year function is defined in both icu and core_functions, but with different overloads. Our auto-loading functionality is currently based on auto-loading entire functions - so that if a function is not found in the catalog, the extension is auto-loaded. With different overloads in different extensions this becomes ambiguous (which one do you auto-load?). In addition, the auto-loading causes weird behavior if only one of the two extensions are loaded - since the correct overload might not be present.

This PR solves this by extending the auto-loading to function overloads. This is accomplished by adding an EXTENSION_FUNCTION_OVERLOADS - which includes specific overloads for functions. On start-up, the extension overloads are registered using a dummy function. In the bind of this dummy function the extension auto-load is attempted - and if successful, the function is loaded from the extension. This also fixes a long-standing issue around auto-loading of ICU that was mainly present in WASM, as ICU introduces a lot of overloads for existing functions which would then result in a binding error when used without ICU, instead of resulting in ICU itself being loaded.

The EXTENSION_FUNCTION_OVERLOADS are automatically generated similar to the functions. If the same function exists in multiple extensions - it is added to EXTENSION_FUNCTION_OVERLOADS instead of to EXTENSION_FUNCTIONS with the corresponding overloads.