fix(android): ensure Appearance change listener does not skip events (facebook#46017)

Summary:
I'm able to reproduce a case when Appearance module methods are called in the following order:

starting point: dark mode enabled
1. call `setColorScheme` light
2. call `getColorScheme`, which sets `colorScheme` to light [here](https://github.com/facebook/react-native/blob/7bb7a6037bd78bbfa6d9e8499973ea921e9c70e1/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/modules/appearance/AppearanceModule.kt#L57)
3. [onConfigurationChanged](https://github.com/facebook/react-native/blob/7bb7a6037bd78bbfa6d9e8499973ea921e9c70e1/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/modules/appearance/AppearanceModule.kt#L82) is called but `if (colorScheme != newColorScheme)` does not evaluate to true, so no event is dispatched to JS. That means JS is not in sync with the native state.

The issue was the `getColorScheme` had a side-effect of setting `colorScheme` private member (not sure what its use was). The fix remembers the last emitted color scheme value and emits event if new value is different.

## Changelog:

[ANDROID] [FIXED] - ensure Appearance change listener does not skip events

Pull Request resolved: facebook#46017

Test Plan: tested locally with RN tester

Reviewed By: NickGerleman

Differential Revision: D62016949

Pulled By: cipolleschi

fbshipit-source-id: b7b5755d38becda655cf376749d9a996daff7e07

Author: vonovak

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/modules/appearance/AppearanceModule.kt

@@ -24,7 +24,7 @@ constructor(
     private val overrideColorScheme: OverrideColorScheme? = null
 ) : NativeAppearanceSpec(reactContext) {
 
-  private var colorScheme = colorSchemeForCurrentConfiguration(reactContext)
+  private var lastEmittedColorScheme: String? = null
 
   /** Optional override to the current color scheme */
   public fun interface OverrideColorScheme {
@@ -42,10 +42,10 @@ constructor(
 
     val currentNightMode =
         context.resources.configuration.uiMode and Configuration.UI_MODE_NIGHT_MASK
-    when (currentNightMode) {
-      Configuration.UI_MODE_NIGHT_NO -> return "light"
-      Configuration.UI_MODE_NIGHT_YES -> return "dark"
-      else -> return "light"
+    return when (currentNightMode) {
+      Configuration.UI_MODE_NIGHT_NO -> "light"
+      Configuration.UI_MODE_NIGHT_YES -> "dark"
+      else -> "light"
     }
   }
 
@@ -54,16 +54,16 @@ constructor(
     // scheme. This covers the scenario when AppCompatDelegate.setDefaultNightMode()
     // is called directly (which can occur in Brownfield apps for example).
     val activity = getCurrentActivity()
-    colorScheme = colorSchemeForCurrentConfiguration(activity ?: getReactApplicationContext())
-    return colorScheme
+    return colorSchemeForCurrentConfiguration(activity ?: getReactApplicationContext())
   }
 
   public override fun setColorScheme(style: String) {
-    when {
-      style == "dark" -> AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES)
-      style == "light" -> AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
-      style == "unspecified" ->
+    when (style) {
+      "dark" -> AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES)
+      "light" -> AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
+      "unspecified" ->
           AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM)
+
     }
   }
 
@@ -79,9 +79,9 @@ constructor(
    */
   public fun onConfigurationChanged(currentContext: Context) {
     val newColorScheme = colorSchemeForCurrentConfiguration(currentContext)
-    if (colorScheme != newColorScheme) {
-      colorScheme = newColorScheme
-      emitAppearanceChanged(colorScheme)
+    if (lastEmittedColorScheme != newColorScheme) {
+      lastEmittedColorScheme = newColorScheme
+      emitAppearanceChanged(newColorScheme)
     }
   }