Parse and expose more style JSON root properties

[kkaefer]

mbgl::style::Parser::parse() should parse the name and metadata root properties out of the style JSON and expose them with accessors on the mbgl::style::Style class. The SDK could read the name of the style aloud in accessibility contexts.

Similarly, root properties such as center and zoom may be useful for establishing a default viewport for the style other than the Null Island default used in the SDK currently. This would enable the developer to set the default viewport once, in Mapbox Studio, and not have to set it again programmatically or in a storyboard.

/cc @jfirebaugh @kkaefer

[kkaefer]

What properties from metadata would you use? It seems like they aren't defined and currently are only used internally by Mapbox Studio. Not having a defined spec for those makes it hard/impossible to expose them.

[mention-bot]

@kkaefer, thanks for your PR! By analyzing this pull request, we identified @jfirebaugh, @1ec5 and @ansis to be potential reviewers.

[kkaefer]

@1ec5 This patch parses the properties, but they aren't yet exposed in the SDK. You can obtain the values with Map::getName(), Map::getDefaultLatLng(), Map::getDefaultZoom(), Map::getDefaultBearing(), and Map::getDefaultPitch().

Do you have any specific use case for metadata values?

[1ec5]

Should this be getStyleName()?

[kkaefer]

Yeah; renamed.

[1ec5]

Do you have any specific use case for metadata values?

No, I figured this would eventually be opened up to developers, but we can definitely leave it out, especially since the structure is undefined.

[1ec5]

👍