[ios] Standardize exception definitions

[friedbunny]

Fixes #7258 by converting stringly-typed exception names into MGLExceptionName-typed constants. This doesn’t attempt to document the exceptions, but that could happen in the future.

/cc @1ec5 @fabian-guerra @julianrex @captainbarbosa

[julianrex]

Great to see these changes!
The only comment I have is: should the exception names be of the form MGLException<Name>? So MGLExceptionAbstractClass instead of MGLAbstractClassException?

[friedbunny]

Should the exception names be of the form MGLException<Name>? So MGLExceptionAbstractClass instead of MGLAbstractClassException?

MGLFooException follows Cocoa’s naming convention for exceptions and is how Foundation names its exceptions.

(This makes sense to me when I think of it in terms of calling our UIView subclass containing a map MGLMapView instead of MGLViewMap.)

[fabian-guerra]

Instead of having a master header with all the exceptions, we will declare on each file the exceptions it throws (if any)? If so, should we document this?

[friedbunny]

@julianrex and I were curious about how this ended up looking in Swift, so:

[friedbunny]

I was copying NSExceptionName, but I’m going to look at replacing this with NS_TYPED_EXTENSIBLE_ENUM on Apple’s recommendation:

You might encounter Objective-C code that uses the older NS_STRING_ENUM and NS_EXTENSIBLE_STRING_ENUM macros, which were used to group string constants. Use NS_TYPED_ENUM and NS_TYPED_EXTENSIBLE_ENUM when grouping related constants of any type, including string constants.

[friedbunny]

Xcode 9 has all of these defined as the same thing, so it’s just cosmetic:

#define NS_STRING_ENUM _NS_TYPED_ENUM
#define NS_EXTENSIBLE_STRING_ENUM _NS_TYPED_EXTENSIBLE_ENUM

#define NS_TYPED_ENUM _NS_TYPED_ENUM
#define NS_TYPED_EXTENSIBLE_ENUM _NS_TYPED_EXTENSIBLE_ENUM

... but let’s still standardize on the new one.

[friedbunny]

Instead of having a master header with all the exceptions, we will declare on each file the exceptions it throws (if any)? If so, should we document this?

Defining non-generic constants close to their main usage sites is generally a good practice, I think, and is something we’ve been doing with other constants, like MGLTileSourceOption and friends. I’ll go through and add a bit of private documentation in MGLTypes to try and make it clear that those are generic exceptions.

[1ec5]

#12640 takes care of the macOS side of this change.