[macOS] Add modifier state to raw key events (#239)

Author: jbg

library/macos/FLEViewController.m

@@ -33,6 +33,12 @@
 
 static const int kDefaultWindowFramebuffer = 0;
 
+// Android KeyEvent constants from https://developer.android.com/reference/android/view/KeyEvent
+static const int kAndroidMetaStateShift = 1 << 0;
+static const int kAndroidMetaStateAlt = 1 << 1;
+static const int kAndroidMetaStateCtrl = 1 << 12;
+static const int kAndroidMetaStateMeta = 1 << 16;
+
 #pragma mark - Private interface declaration.
 
 /**
@@ -376,6 +382,12 @@ - (void)dispatchKeyEvent:(NSEvent *)event ofType:(NSString *)type {
     @"keymap" : @"android",
     @"type" : type,
     @"keyCode" : @(event.keyCode),
+    @"metaState" : @(
+      ((event.modifierFlags & NSEventModifierFlagShift) ? kAndroidMetaStateShift : 0) |
+      ((event.modifierFlags & NSEventModifierFlagOption) ? kAndroidMetaStateAlt : 0) |
+      ((event.modifierFlags & NSEventModifierFlagControl) ? kAndroidMetaStateCtrl : 0) |
+      ((event.modifierFlags & NSEventModifierFlagCommand) ? kAndroidMetaStateMeta : 0)
+    )
   }];
 }