fix: the launcher does not offer its own display as a second screen (#889)

* fix: the launcher does not offer its own display as a second screen

MainActivity asked for the second-screen candidates with the default
display as the primary one. When the launcher is itself shown on another
display (DeX, an external monitor), that display was listed as a second
screen. Pass the Activity's own display id, as SessionActivity already does.

* fix: read the Activity display only on API 30 and newer

minSdk is 26 and Activity.getDisplay needs API 30. Use windowManager.defaultDisplay below that.

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Co-authored-by: ovurrsl <ovurrsl@users.noreply.github.com>

app/src/main/java/com/droiddeck/launcher/MainActivity.kt

@@ -1050,7 +1050,9 @@ class MainActivity : ComponentActivity() {
 
     private fun refreshSecondScreenDisplays() {
         if (!::displayManager.isInitialized) return
-        secondScreenDisplays = SecondScreenDisplays.available(displayManager)
+        // The launcher can itself be shown on a non-default display (DeX, an external monitor); that one is not a "second screen".
+        val ownDisplayId = if (android.os.Build.VERSION.SDK_INT >= 30) display?.displayId ?: android.view.Display.DEFAULT_DISPLAY else @Suppress("DEPRECATION") windowManager.defaultDisplay.displayId
+        secondScreenDisplays = SecondScreenDisplays.available(displayManager, ownDisplayId)
     }
 
     private fun launchAndroidApp(app: HomeApp.LaunchableApp, displayId: Int?) {