Source attribution should be object-oriented

[1ec5]

MGLTileSet’s attribution property – which may soon live on MGLTileSource; see #7360 – should be an array of objects containing structured attribution information. We can use the MGLAttributionInfo class being added in #5999 to represent a single attribution item.

The current MGLTileSet.attribution property is a single string containing HTML code. This encourages developers to manually craft HTML strings, which can be error-prone. It also means any developer who wants to make sense of a preexisting attribution string would have to parse it as HTML. Done incorrectly, both operations can be avenues for HTML injection. Since #5999 already parses the HTML source code into structured attribution, I don’t think there’s really a use case for working with the raw source code as opposed to, say, an attributed string (which can always be converted back to HTML if needed).

/cc @boundsj @friedbunny

[1ec5]

Someday, once mapbox/tilejson-spec#20 is implemented, the SDKs will be able to take advantage of structured attribution in TileJSON with minimal changes and likely no changes to public-facing API.

[1ec5]

We’re pulling this refactoring into the v3.4.0 milestone because most of the pieces are already in place and because we don’t want to have to make a backwards-incompatible change or deprecate a symbol just to expose MGLAttributionInfo publicly. This change will probably occur as part of #7377.

[1ec5]

Fixed in #7377 on the iOS SDK v3.4.0 release branch.