fix: moving a mouse no longer recomposes the whole session overlay

The session overlay read the cursor position while composing, so every mouse
move rebuilt the overlay (HUD, glasses hints and the rest) on the UI thread.
The cursor now reads its position while drawing, so a move only redraws the
cursor.

Part of #1247

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

@@ -636,7 +636,7 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
                 }
             } else {
             com.droiddeck.launcher.ui.FocusGlideHost(androidx.compose.ui.Modifier.fillMaxSize()) {
-                CursorOverlay(cursorPos, cursorVisible, resources.displayMetrics.density,
+                CursorOverlay({ cursorPos }, cursorVisible, resources.displayMetrics.density,
                     cursorImage, cursorHotX, cursorHotY, cursorImageScale)
                 if (hud.text.isNotEmpty()) HudText(hud.text)
                 if (glassesOutputActive && !loading.visible) com.droiddeck.launcher.ui.GlassesPlayingHint(glasses.model)

app/src/main/java/com/droiddeck/launcher/ui/CursorOverlay.kt

@@ -13,11 +13,12 @@ import androidx.compose.ui.graphics.drawscope.Stroke
 
 @Composable
 fun CursorOverlay(
-    position: Offset, visible: Boolean, scale: Float,
+    positionOf: () -> Offset, visible: Boolean, scale: Float,
     image: ImageBitmap? = null, hotX: Int = 0, hotY: Int = 0, imageScale: Float = 1f,
 ) {
     if (!visible) return
     Canvas(modifier = Modifier.fillMaxSize()) {
+        val position = positionOf()
         if (image != null) {
             val w = (image.width * imageScale).toInt().coerceAtLeast(1)
             val h = (image.height * imageScale).toInt().coerceAtLeast(1)