[image_picker] Switch to Kotlin Pigeon (#11504)

Replaces the Java Pigeon generator with the Kotlin Pigeon generator, and adjusts the project accordingly:
- Adds Kotlin build setings to Gradle.
- Updates API signatures for Kotlin/Java differences.
- Adds generic Java/Kotlin compat shim to create Result objects from Java, since those haven't been added to the Pigeon generator yet.
- Updates tests to use constructors instead of builders, since the Kotlin generator doesn't create builders.
- Updates tests to use a Java/Kotlin compat shim to read Kotlin Result values, instead of mocking the Java Pigeon response object.

Part of flutter/flutter#158287

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: stuartmorgan-g

packages/image_picker/image_picker_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.8.13+17
+
+* Updates internal implementation to use Kotlin Pigeon.
+
 ## 0.8.13+16
 
 * Bumps androidx.core:core from 1.17.0 to 1.18.0.

packages/image_picker/image_picker_android/android/build.gradle.kts

@@ -1,14 +1,18 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 group = "io.flutter.plugins.imagepicker"
 version = "1.0-SNAPSHOT"
 
 buildscript {
+    val kotlinVersion = "2.3.20"
     repositories {
         google()
         mavenCentral()
     }
 
     dependencies {
         classpath("com.android.tools.build:gradle:8.13.1")
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
     }
 }
 
@@ -21,6 +25,13 @@ allprojects {
 
 plugins {
     id("com.android.library")
+    id("kotlin-android")
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget = JvmTarget.fromTarget(JavaVersion.VERSION_17.toString())
+    }
 }
 
 android {

packages/image_picker/image_picker_android/android/src/main/java/io/flutter/plugins/imagepicker/ImagePickerCache.java

@@ -75,7 +75,7 @@ private void setType(String type) {
     prefs.edit().putString(SHARED_PREFERENCE_TYPE_KEY, type).apply();
   }
 
-  void saveDimensionWithOutputOptions(Messages.ImageSelectionOptions options) {
+  void saveDimensionWithOutputOptions(ImageSelectionOptions options) {
     final SharedPreferences prefs =
         context.getSharedPreferences(SHARED_PREFERENCES_NAME, Context.MODE_PRIVATE);
     SharedPreferences.Editor editor = prefs.edit();
@@ -87,7 +87,7 @@ void saveDimensionWithOutputOptions(Messages.ImageSelectionOptions options) {
       editor.putLong(
           SHARED_PREFERENCE_MAX_HEIGHT_KEY, Double.doubleToRawLongBits(options.getMaxHeight()));
     }
-    editor.putInt(SHARED_PREFERENCE_IMAGE_QUALITY_KEY, options.getQuality().intValue());
+    editor.putInt(SHARED_PREFERENCE_IMAGE_QUALITY_KEY, (int) options.getQuality());
     editor.apply();
   }
 
@@ -146,13 +146,12 @@ Map<String, Object> getCacheMap() {
     }
 
     if (prefs.contains(SHARED_PREFERENCE_ERROR_CODE_KEY)) {
-      final Messages.CacheRetrievalError.Builder error = new Messages.CacheRetrievalError.Builder();
-      error.setCode(prefs.getString(SHARED_PREFERENCE_ERROR_CODE_KEY, ""));
+      final CacheRetrievalError error =
+          new CacheRetrievalError(
+              prefs.getString(SHARED_PREFERENCE_ERROR_CODE_KEY, ""),
+              prefs.getString(SHARED_PREFERENCE_ERROR_MESSAGE_KEY, null));
       hasData = true;
-      if (prefs.contains(SHARED_PREFERENCE_ERROR_MESSAGE_KEY)) {
-        error.setMessage(prefs.getString(SHARED_PREFERENCE_ERROR_MESSAGE_KEY, ""));
-      }
-      resultMap.put(MAP_KEY_ERROR, error.build());
+      resultMap.put(MAP_KEY_ERROR, error);
     }
 
     if (hasData) {
@@ -161,8 +160,8 @@ Map<String, Object> getCacheMap() {
         resultMap.put(
             MAP_KEY_TYPE,
             typeValue.equals(MAP_TYPE_VALUE_VIDEO)
-                ? Messages.CacheRetrievalType.VIDEO
-                : Messages.CacheRetrievalType.IMAGE);
+                ? CacheRetrievalType.VIDEO
+                : CacheRetrievalType.IMAGE);
       }
       if (prefs.contains(SHARED_PREFERENCE_MAX_WIDTH_KEY)) {
         final long maxWidthValue = prefs.getLong(SHARED_PREFERENCE_MAX_WIDTH_KEY, 0);