Geometric types should conform to common protocol that converts to Geometry

GEOSwift defines a GeometryConvertible protocol that makes it possible to initialize a Feature without redundantly specifying both the Geometry case and the geometric type’s initializer at the same time. Turf’s GeoJSONObject and Geometry enumerations should have something similar. For example:

var geoJSON = Feature(geometry: .point(Point(coordinate)))

would become simply:

var geoJSON = Feature(geometry: Point(coordinate))

It’s similar to the initializers and literals that #154 added to JSONValue, but this protocol distributes the implementation across each type:

turf-swift/Sources/Turf/JSON.swift

Lines 49 to 52 in 007896b

    
           /// Initializes a JSON value representing the given Boolean value. 
        
           public init(_ bool: Bool) { 
        
               self = .boolean(bool) 
        
           }

/cc @macdrevx

A similar JSONValueConvertible protocol might eliminate a major backwards-incompatible change that arose in #154, making both syntaxes equivalent again:

feature.properties = [
    "literal": "Jason",
    "non-literal": .string(name),
]

feature.properties = [
    "literal": "Jason",
    "non-literal": name,
]

A similar JSONValueConvertible protocol might eliminate a major backwards-incompatible change that arose in #154, making both syntaxes equivalent again

I’ve been trying various gymnastics but haven’t managed to make this work without making [String: Any?] conform to ExpressibleByArrayLiteral, which would be overbroad.

A similar JSONValueConvertible protocol might eliminate a major backwards-incompatible change that arose in #154, making both syntaxes equivalent again

Now tracking this feature separately in #163.

	/// Initializes a JSON value representing the given Boolean value.
	public init(_ bool: Bool) {
	self = .boolean(bool)
	}