UI: Use spacers instead of widgets in macOS Permissions UI

The macOS Permissions dialog was using empty widgets to force other
widgets into position. Instead, use horizontal spacers.

UI/forms/OBSPermissions.ui

@@ -145,7 +145,17 @@
               <number>25</number>
              </property>
              <item>
-              <widget class="QWidget"/>
+              <spacer name="horizontalSpacer">
+               <property name="orientation">
+                <enum>Qt::Horizontal</enum>
+               </property>
+               <property name="sizeHint" stdset="0">
+                <size>
+                 <width>40</width>
+                 <height>20</height>
+                </size>
+               </property>
+              </spacer>
              </item>
              <item>
               <widget class="QPushButton" name="capturePermissionButton">
@@ -211,7 +221,17 @@
               <number>25</number>
              </property>
              <item>
-              <widget class="QWidget"/>
+              <spacer name="horizontalSpacer_2">
+               <property name="orientation">
+                <enum>Qt::Horizontal</enum>
+               </property>
+               <property name="sizeHint" stdset="0">
+                <size>
+                 <width>40</width>
+                 <height>20</height>
+                </size>
+               </property>
+              </spacer>
              </item>
              <item>
               <widget class="QPushButton" name="videoPermissionButton">
@@ -274,7 +294,17 @@
               <number>25</number>
              </property>
              <item>
-              <widget class="QWidget"/>
+              <spacer name="horizontalSpacer_3">
+               <property name="orientation">
+                <enum>Qt::Horizontal</enum>
+               </property>
+               <property name="sizeHint" stdset="0">
+                <size>
+                 <width>40</width>
+                 <height>20</height>
+                </size>
+               </property>
+              </spacer>
              </item>
              <item>
               <widget class="QPushButton" name="audioPermissionButton">
@@ -340,7 +370,17 @@
               <number>25</number>
              </property>
              <item>
-              <widget class="QWidget"/>
+              <spacer name="horizontalSpacer_4">
+               <property name="orientation">
+                <enum>Qt::Horizontal</enum>
+               </property>
+               <property name="sizeHint" stdset="0">
+                <size>
+                 <width>40</width>
+                 <height>20</height>
+                </size>
+               </property>
+              </spacer>
              </item>
              <item>
               <widget class="QPushButton" name="accessibilityPermissionButton">