Resolve issue where location value is declared after observer is noti…

…fied (#1287)

* declaring value before observer is notified and adding tests

Sources/MapboxMaps/Foundation/ObservableValue.swift

@@ -15,10 +15,10 @@ internal final class ObservableValue<Value> where Value: Equatable {
         guard newValue != value else {
             return
         }
+        value = newValue
         observers.forEach { (observer) in
             observer.invokeHandler(with: newValue)
         }
-        value = newValue
     }
 
     internal func observe(with handler: @escaping (Value) -> Bool) -> Cancelable {

Tests/MapboxMapsTests/Viewport/Helpers/ObservableValueTests.swift

@@ -56,6 +56,16 @@ final class ObservableValueTests: XCTestCase {
         XCTAssertEqual(handlerStub.invocations.map(\.parameters), [value])
     }
 
+    func testValueUpdatedBeforeNotifyingObservers() {
+        let handlerStub = Stub<Int, Bool>(defaultReturnValue: true)
+        handlerStub.defaultSideEffect = { invocation in
+            XCTAssertEqual(self.observableValue.value, invocation.parameters)
+        }
+        _ = observableValue.observe(with: handlerStub.call(with:))
+
+        update()
+    }
+
     func testHandlerReturnsTrueToContinueAndFalseToUnsubscribe() {
         let handlerStub = Stub<Int, Bool>(defaultReturnValue: false)
         handlerStub.returnValueQueue = [true, true]