Bug 1886374 - On macOS, disable camera gestures by default. r=mac-reviewers,bradwerth

As documented in AVCaptureDevice.h in MacOSX14.4.sdk:
  By default, gesture detection is enabled.  As of iOS 17.4 and macOS 14.4, applications can control the default value of this property by adding the following key to their Info.plist:
      <key>NSCameraReactionEffectGesturesEnabledDefault</key>
  A value of true enables gesture detection and a value of false disables it, until such time that the user makes their own selection in Control Center.

Differential Revision: https://phabricator.services.mozilla.com/D205227

Author: Pehrsons

browser/app/macbuild/Contents/Info.plist.in

@@ -291,5 +291,8 @@
 
   <key>NSMicrophoneUsageDescription</key>
   <string>Only sites you allow within @MAC_APP_NAME@ will be able to use the microphone.</string>
+
+  <key>NSCameraReactionEffectGesturesEnabledDefault</key>
+  <false/>
 </dict>
 </plist>