android: Min SDK level to 21 (#10505)

Google Play has dropped support for SDK levels 19 and 20 and so can we.

README.md

@@ -20,7 +20,7 @@ gRPC-Java - An RPC library and framework
 Supported Platforms
 -------------------
 
-gRPC-Java supports Java 8 and later. Android minSdkVersion 19 (KitKat) and
+gRPC-Java supports Java 8 and later. Android minSdkVersion 21 (Lollipop) and
 later are supported with [Java 8 language desugaring][android-java-8].
 
 TLS usage on Android typically requires Play Services Dynamic Security Provider.

android-interop-testing/build.gradle

@@ -34,7 +34,10 @@ android {
 
     defaultConfig {
         applicationId "io.grpc.android.integrationtest"
-        minSdkVersion 19
+        // Held back to 20 as Gradle fails to build at the 21 level. This is
+        // presumably a Gradle bug that can be revisited later.
+        // Maybe this issue: https://github.com/gradle/gradle/issues/20778
+        minSdkVersion 20
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

android-interop-testing/src/main/AndroidManifest.xml

@@ -1,10 +1,12 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android" >
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools">
 
     <uses-permission android:name="android.permission.INTERNET" />
     <!-- For UDS -->
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
+    <uses-sdk tools:overrideLibrary="io.grpc.android"/>
 
     <application
         android:allowBackup="true"

android/build.gradle

@@ -15,7 +15,7 @@ android {
     compileSdkVersion 33
     defaultConfig {
         consumerProguardFiles "proguard-rules.txt"
-        minSdkVersion 19
+        minSdkVersion 21
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

binder/build.gradle

@@ -13,7 +13,7 @@ android {
         targetCompatibility 1.8
     }
     defaultConfig {
-        minSdkVersion 19
+        minSdkVersion 21
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

cronet/build.gradle

@@ -15,7 +15,7 @@ android {
     namespace 'io.grpc.cronet'
     compileSdkVersion 33
     defaultConfig {
-        minSdkVersion 19
+        minSdkVersion 21
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

examples/android/clientcache/app/build.gradle

@@ -10,7 +10,7 @@ android {
 
     defaultConfig {
         applicationId "io.grpc.clientcacheexample"
-        minSdkVersion 19
+        minSdkVersion 21
         targetSdkVersion 33
         multiDexEnabled true
         versionCode 1

examples/android/helloworld/app/build.gradle

@@ -10,7 +10,7 @@ android {
 
     defaultConfig {
         applicationId "io.grpc.helloworldexample"
-        minSdkVersion 19
+        minSdkVersion 21
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

examples/android/routeguide/app/build.gradle

@@ -10,7 +10,7 @@ android {
 
     defaultConfig {
         applicationId "io.grpc.routeguideexample"
-        minSdkVersion 19
+        minSdkVersion 21
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"