Drop support for Android API levels 21-22 (#12676)

Google Play Services needs min Android API level of 23 (Android 6.0
Marshmallow).

Fixes [#11474](#11474).

Author: kannanjgithub

README.md

@@ -20,7 +20,7 @@ gRPC-Java - An RPC library and framework
 Supported Platforms
 -------------------
 
-gRPC-Java supports Java 8 and later. Android minSdkVersion 21 (Lollipop) and
+gRPC-Java supports Java 8 and later. Android minSdkVersion 23 (Marshmallow) and
 later are supported with [Java 8 language desugaring][android-java-8].
 
 TLS usage on Android typically requires Play Services Dynamic Security Provider.

android/build.gradle

@@ -14,7 +14,7 @@ android {
     }
     compileSdkVersion 34
     defaultConfig {
-        minSdkVersion 22
+        minSdkVersion 23
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

binder/build.gradle

@@ -13,7 +13,7 @@ android {
         targetCompatibility 1.8
     }
     defaultConfig {
-        minSdkVersion 22
+        minSdkVersion 23
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

cronet/build.gradle

@@ -14,7 +14,7 @@ android {
     namespace = 'io.grpc.cronet'
     compileSdkVersion 33
     defaultConfig {
-        minSdkVersion 22
+        minSdkVersion 23
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

cronet/src/main/java/io/grpc/cronet/CronetChannelBuilder.java

@@ -21,7 +21,6 @@
 import static io.grpc.internal.GrpcUtil.DEFAULT_MAX_MESSAGE_SIZE;
 
 import android.net.Network;
-import android.os.Build;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.util.concurrent.MoreExecutors;
@@ -340,9 +339,7 @@ public BidirectionalStream.Builder newBidirectionalStreamBuilder(
         builder.setTrafficStatsUid(trafficStatsUid);
       }
       if (network != null) {
-        if (Build.VERSION.SDK_INT >= 23) {
-          builder.bindToNetwork(network.getNetworkHandle());
-        }
+        builder.bindToNetwork(network.getNetworkHandle());
       }
       return builder;
     }

examples/android/helloworld/app/build.gradle

@@ -10,7 +10,7 @@ android {
 
     defaultConfig {
         applicationId "io.grpc.helloworldexample"
-        minSdkVersion 21
+        minSdkVersion 23
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"

examples/android/routeguide/app/build.gradle

@@ -10,7 +10,7 @@ android {
 
     defaultConfig {
         applicationId "io.grpc.routeguideexample"
-        minSdkVersion 21
+        minSdkVersion 23
         targetSdkVersion 33
         versionCode 1
         versionName "1.0"