Update compileSdkVersion in the Android app templates to Android P (#26444)

Fixes https://github.com/flutter/flutter/issues/25703

packages/flutter_tools/templates/app/android-java.tmpl/app/build.gradle.tmpl

@@ -25,7 +25,7 @@ apply plugin: 'com.android.application'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 
     lintOptions {
         disable 'InvalidPackage'

packages/flutter_tools/templates/app/android-kotlin.tmpl/app/build.gradle.tmpl

@@ -26,7 +26,7 @@ apply plugin: 'kotlin-android'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 
     sourceSets {
         main.java.srcDirs += 'src/main/kotlin'

packages/flutter_tools/templates/module/android/host_app_common/app.tmpl/build.gradle.tmpl

@@ -3,7 +3,7 @@ def flutterPluginVersion = 'managed'
 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 
     compileOptions {
         sourceCompatibility 1.8

packages/flutter_tools/templates/module/android/library/Flutter.tmpl/build.gradle.tmpl

@@ -27,7 +27,7 @@ apply plugin: 'com.android.library'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 
     defaultConfig {
         minSdkVersion 16

packages/flutter_tools/templates/plugin/android-java.tmpl/build.gradle.tmpl

@@ -22,7 +22,7 @@ rootProject.allprojects {
 apply plugin: 'com.android.library'
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 
     defaultConfig {
         minSdkVersion 16

packages/flutter_tools/templates/plugin/android-kotlin.tmpl/build.gradle.tmpl

@@ -25,7 +25,7 @@ apply plugin: 'com.android.library'
 apply plugin: 'kotlin-android'
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 
     sourceSets {
         main.java.srcDirs += 'src/main/kotlin'

packages/flutter_tools/test/project_test.dart

@@ -478,7 +478,7 @@ String gradleFileWithApplicationId(String id) {
   return '''
 apply plugin: 'com.android.application'
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 
     defaultConfig {
         applicationId '$id'
@@ -495,7 +495,7 @@ version '1.0-SNAPSHOT'
 apply plugin: 'com.android.library'
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 28
 }
 ''';
 }