[ios] Fix type narrowing issue with MGLOpenGLStyleLayer projection matrix (#11664)

`CATransform3D`'s matrix is internally typed as `CGFloat`, which we were implicitly casting to from `double`.... except that the `-Wc++11-narrowing` flag disallows implicit narrowing casts and we need `double` precision, anyway.

* [ios, macos] Use MGLMatrix4 a 4x4 double matrix for MGLOpenGLStyleLayer projection matrix.

* [ios, macos] Don't use union for MGLMatrix4

platform/darwin/src/MGLGeometry.h

@@ -24,6 +24,14 @@ typedef struct __attribute__((objc_boxable)) MGLMapPoint {
     CGFloat zoomLevel;
 } MGLMapPoint;
 
+/* Defines a 4x4 matrix. */
+typedef struct MGLMatrix4 {
+    double m00, m01, m02, m03;
+    double m10, m11, m12, m13;
+    double m20, m21, m22, m23;
+    double m30, m31, m32, m33;
+} MGLMatrix4;
+
 /**
  Creates a new `MGLCoordinateSpan` from the given latitudinal and longitudinal
  deltas.

platform/darwin/src/MGLGeometry.mm

@@ -111,3 +111,14 @@ MGLMapPoint MGLMapPointForCoordinate(CLLocationCoordinate2D coordinate, double z
     mbgl::Point<double> projectedCoordinate = mbgl::Projection::project(MGLLatLngFromLocationCoordinate2D(coordinate), std::pow(2.0, zoomLevel));
     return MGLMapPointMake(projectedCoordinate.x, projectedCoordinate.y, zoomLevel);
 }
+
+MGLMatrix4 MGLMatrix4Make(std::array<double, 16>  array) {
+    MGLMatrix4 mat4 = {
+        .m00 = array[0], .m01 = array[1], .m02 = array[2], .m03 = array[3],
+        .m10 = array[4], .m11 = array[5], .m12 = array[6], .m13 = array[7],
+        .m20 = array[8], .m21 = array[9], .m22 = array[10], .m23 = array[11],
+        .m30 = array[12], .m31 = array[13], .m32 = array[14], .m33 = array[15]
+    };
+    return mat4;
+}
+

platform/darwin/src/MGLGeometry_Private.h

@@ -128,3 +128,5 @@ MGLRadianCoordinate2D MGLRadianCoordinateAtDistanceFacingDirection(MGLRadianCoor
 CLLocationDirection MGLDirectionBetweenCoordinates(CLLocationCoordinate2D firstCoordinate, CLLocationCoordinate2D secondCoordinate);
 
 CGPoint MGLPointRounded(CGPoint point);
+
+MGLMatrix4 MGLMatrix4Make(std::array<double, 16> mat);

platform/darwin/src/MGLOpenGLStyleLayer.h

@@ -5,6 +5,7 @@
 #import "MGLFoundation.h"
 #import "MGLStyleValue.h"
 #import "MGLStyleLayer.h"
+#import "MGLGeometry.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -18,7 +19,7 @@ typedef struct MGLStyleLayerDrawingContext {
     CLLocationDirection direction;
     CGFloat pitch;
     CGFloat fieldOfView;
-    CATransform3D projectionMatrix;
+    MGLMatrix4 projectionMatrix;
 } MGLStyleLayerDrawingContext;
 
 MGL_EXPORT

platform/darwin/src/MGLOpenGLStyleLayer.mm

@@ -3,21 +3,11 @@
 #import "MGLMapView_Private.h"
 #import "MGLStyle_Private.h"
 #import "MGLStyleLayer_Private.h"
+#import "MGLGeometry_Private.h"
 
 #include <mbgl/style/layers/custom_layer.hpp>
 #include <mbgl/math/wrap.hpp>
 
-
-CATransform3D CATransform3DMake(std::array<double, 16> array) {
-    CATransform3D t = {
-        .m11 = array[0], .m12 = array[1], .m13 = array[2], .m14 = array[3],
-        .m21 = array[4], .m22 = array[5], .m23 = array[6], .m24 = array[7],
-        .m31 = array[8], .m32 = array[9], .m33 = array[10], .m34 = array[11],
-        .m41 = array[12], .m42 = array[13], .m43 = array[14], .m44 = array[15]
-    };
-    return t;
-}
-
 class MGLOpenGLLayerHost : public mbgl::style::CustomLayerHost {
 public:
     MGLOpenGLLayerHost(MGLOpenGLStyleLayer *styleLayer) {
@@ -42,7 +32,7 @@ public:
             .direction = mbgl::util::wrap(params.bearing, 0., 360.),
             .pitch = static_cast<CGFloat>(params.pitch),
             .fieldOfView = static_cast<CGFloat>(params.fieldOfView),
-            .projectionMatrix = CATransform3DMake(params.projectionMatrix)
+            .projectionMatrix = MGLMatrix4Make(params.projectionMatrix)
         };
         [layer drawInMapView:layer.style.mapView withContext:drawingContext];
     }