Add ToStringOptions.hideFunctionSelfArgument

[JohnnyMorganz]

Adds an option to hide the self: type argument as the first argument in the string representation of a named function type var if the ftv hasSelf.

Also added in a test for the original output (i.e., if the option was disabled)

I didn't apply this option in the normal Luau::toString() function, just the Luau::toStringNamedFunction() one (for my usecase, that is enough + I felt like a named function would include the method colon : to signify self). If this is unintuitive, I can also add it to the general Luau::toString() function.

[alexmccord]

Thanks! I think it's okay to leave it out of Luau::toString().

[andyfriesen]

It's a little bit weird that, when this option is set, the test method still shows a generic a that is not actually used in any of the displayed arguments or return type.

Probably okay, but something to be aware of.

[JohnnyMorganz]

It's a little bit weird that, when this option is set, the test method still shows a generic a that is not actually used in any of the displayed arguments or return type.

Probably okay, but something to be aware of.

Valid point, I noticed this when I wrote the test (missed it out the first time). Wasn't sure on what to do here - I assume if we wanted to also hide this it would introduce quite a bit more complexity to the generics stringifier (need to check which generic to remove and only remove it if its not referenced anywhere)