Add explicit imports for CoreGraphics in files which use it.

PiperOrigin-RevId: 642471770

Author: Nobody

components/OverlayWindow/src/MDCOverlayWindow.m

@@ -14,6 +14,7 @@
 
 #import "MDCOverlayWindow.h"
 
+#import <CoreGraphics/CoreGraphics.h>
 #import <objc/runtime.h>
 
 #import "MDCAvailability.h"

components/OverlayWindow/tests/unit/OverlayWindowInitTest.m

@@ -12,10 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#import <CoreGraphics/CoreGraphics.h>
 #import <XCTest/XCTest.h>
 
-#import "MaterialAvailability.h"
-#import "MaterialOverlayWindow.h"
+#import "MDCAvailability.h"
+#import "MDCOverlayWindow.h"
 
 @interface MockOverlayWindow : MDCOverlayWindow