Migrate most tests to the module system

[jathak]

This migrates most tests that aren't explicitly testing @import or global built-in functions to instead use @use and the sass: modules.

This was done using a combination of a new migrate.ts script that can run the Sass migrator over a spec directory and some manual changes and refactorings. There are probably some tests that could have been migrated that this misses because there were some directories I avoided running the migrator over to avoid accidentally changing a test that's actually explicitly testing @import, but this should at least minimize additional migration and new warnings we need to add when we actually deprecate @import and global built-in functions.

The spec/core_functions/module directory has been replaced with spec/core_functions/global, which similarly contains minimal tests for the global versions of each built-in function now that their full functionality is tested using the module system versions.

[nex3]

For functions like this that are just translated into other, more general functions, it probably makes sense to omit them from the new module system tests entirely and have a small global test to verify that the name still works.

[jathak]

Removed the detailed tests for the color.adjust shorthands. The basic tests for the global versions are already in spec/core_functions/global/color and spec/core_functions/color/adjust_color/error/missing_globals tests that the functions that were removed or changed names in the module system don't exist in the color module.