[swift2objc] Extend Builtin Declarations (mainly builtin protocols)

[nikeokoronkwo]

This issue is to add more builtin declarations to the ones already existing in the swift2objc tool:
A few of the main categories of declarations to add are here

Inbuilt Protocols

Swift has a set of inbuilt Core Protocols that can be used by classes, structs, other protocols and generics in type constraints. A few common ones are: Hashable, Numeric, Collection, Error etc.

When making use of such protocols in classes, the protocol implementations are not automatically added to the symbol graph (although they are present, like other inbuilt types like String), and so would need to be added as a builtin declaration.

More Inbuilt Types

A few more types may need to be added, like Dictionary, Array, Set, Slice, etc. Some of these types also make use of generics

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Hopefully by the end of this issue a good amount of the builtin declarations will be present.
A full list of the builtin types in the swift standard library can be found here: https://developer.apple.com/documentation/swift/swift-standard-library

[nikeokoronkwo]

There are a lot of items under the Swift Standard Library, so we might not import all of them. However, it would be helpful to layout the groundwork for such so that if we encounter any libraries containing types not included here, they can easily be added.

This would mean dropping the current enum approach for a more inclusive approach that can include other types like protocols, enums and more. By the way, most swift types are actually structs under the hood, and some even have nested declarations (e.g Swift.UTF16View), which need to be considered, which is why the enum approach would need to be dropped.

[liamappelbe]

This would mean dropping the current enum approach for a more inclusive approach that can include other types like protocols, enums and more.

Yeah, I was working on another refactor and found that I needed to change BuiltInDeclaration to a class. I'll try and get that refactor into a PR today.

[liamappelbe]

When making use of such protocols in classes, the protocol implementations are not automatically added to the symbol graph (although they are present, like other inbuilt types like String), and so would need to be added as a builtin declaration.

What exactly is going on with these protocols? Where are they defined? My hunch is they're not actually built-in, but are defined in Foundation. If that's the case, then instead of adding these protocols as built-ins, we'll be parsing them automatically once #1774 is implemented.

[nikeokoronkwo]

When making use of such protocols in classes, the protocol implementations are not automatically added to the symbol graph (although they are present, like other inbuilt types like String), and so would need to be added as a builtin declaration.

What exactly is going on with these protocols? Where are they defined? My hunch is they're not actually built-in, but are defined in Foundation. If that's the case, then instead of adding these protocols as built-ins, we'll be parsing them automatically once #1774 is implemented.

The protocols are actually built in as a part of the Swift Standard Library, and are actually separate from Foundation. Some protocols that are in the standard library are: Collection, Hashable, Numeric, Equatable and more.

Foundation has its own set of protocols, structs and other declarations. Some protocols in the Foundation library are: DataProtocol, NSFastEnumeration