Parse Mac OS X as a Platform

Closes #4700

Author: shs96c

java/client/src/org/openqa/selenium/Platform.java

@@ -84,7 +84,7 @@ public Platform family() {
     }
   },
 
-  MAC("mac", "darwin", "macOS", "os x") {
+  MAC("mac", "darwin", "macOS", "mac os x", "os x") {
     @Override
     public Platform family() {
       return null;

java/client/test/org/openqa/selenium/PlatformTest.java

@@ -151,6 +151,11 @@ public void testWindowsIsWindows() {
     assertEquals(Platform.fromString("windows"), Platform.WINDOWS);
   }
 
+  @Test
+  public void canParseMacOsXCorrectly() {
+    assertEquals(Platform.MAC, Platform.fromString("Mac OS X"));
+  }
+
   private void assertAllAre(Platform platform, String... osNames) {
     for (String osName : osNames) {
       Platform seen = Platform.extractFromSysProperty(osName);