Sync clipboard in 'onWindowFocusChanged()' instead of 'onResume()'

Since Android 10, multiple activities can simultaneously be in resumed state.
Specifically in multi-window mode, onPause()/onResume() are not called when
window focus changes, because activity is never paused.
So now we use onWindowFocusChanged() as a signal to sync clipboard.

Ref: https://source.android.com/docs/core/display/multi_display/multi-resume
GitHub issue: #62 & #120

app/src/main/java/com/gaurav/avnc/ui/vnc/VncActivity.kt

@@ -109,11 +109,6 @@ class VncActivity : AppCompatActivity() {
         viewModel.state.observe(this) { onClientStateChanged(it) }
     }
 
-    override fun onResume() {
-        super.onResume()
-        viewModel.sendClipboardText()
-    }
-
     override fun onStart() {
         super.onStart()
         binding.frameView.onResume()
@@ -414,7 +409,10 @@ class VncActivity : AppCompatActivity() {
 
     override fun onWindowFocusChanged(hasFocus: Boolean) {
         super.onWindowFocusChanged(hasFocus)
-        if (hasFocus) updateSystemUiVisibility()
+        if (hasFocus) {
+            updateSystemUiVisibility()
+            viewModel.sendClipboardText()
+        }
     }