NotificationChannel.LockscreenVisibility is NotificationVisibility (#8)

Context: https://bugzilla.xamarin.com/show_bug.cgi?id=58895

Change the type of `Android.App.NotificationChannel.LockscreenVisibility`
from `int` to `NotificationVisibility`.

Author: atsushieno

reference/Mono.Android.xml

@@ -1354,7 +1354,7 @@
       </attribute>
       <attribute name="System.Reflection.AssemblyInformationalVersionAttribute">
         <properties>
-          <property name="InformationalVersion" value="7.4.99.72; git-rev-head:58bb714; git-branch:api-o-enumification" />
+          <property name="InformationalVersion" value="7.4.99.107; git-rev-head:3b5955d; git-branch:master" />
         </properties>
       </attribute>
       <attribute name="System.Reflection.AssemblyProductAttribute">
@@ -74825,9 +74825,9 @@
                   </method>
                 </methods>
               </property>
-              <property name="LockscreenVisibility" attrib="0" ptype="System.Int32">
+              <property name="LockscreenVisibility" attrib="0" ptype="Android.App.NotificationVisibility">
                 <methods>
-                  <method name="get_LockscreenVisibility()" attrib="2182" returntype="System.Int32">
+                  <method name="get_LockscreenVisibility()" attrib="2182" returntype="Android.App.NotificationVisibility">
                     <attributes>
                       <attribute name="Android.Runtime.RegisterAttribute">
                         <properties>
@@ -74838,7 +74838,7 @@
                     </attributes>
                     <parameters />
                   </method>
-                  <method name="set_LockscreenVisibility(System.Int32)" attrib="2182" returntype="System.Void">
+                  <method name="set_LockscreenVisibility(Android.App.NotificationVisibility)" attrib="2182" returntype="System.Void">
                     <attributes>
                       <attribute name="Android.Runtime.RegisterAttribute">
                         <properties>
@@ -74848,7 +74848,7 @@
                       </attribute>
                     </attributes>
                     <parameters>
-                      <parameter name="value" position="0" attrib="0" type="System.Int32" />
+                      <parameter name="value" position="0" attrib="0" type="Android.App.NotificationVisibility" />
                     </parameters>
                   </method>
                 </methods>