upgrade gradle plugins, AGP to 7, and others

AGP (Android Gradle Plugin) version 7 requires Java 11 to run,
however we don't want our SDK to require that have of a version so we
set  sourceCompatibility & targetCompatibility to account for that.

Upgraded googleServicesGradlePluginVersion to ensure we are testing with
the latest.
Upgraded onesignalGradlePluginVersion to match our latest version range

Author: jkasten2

OneSignalSDK/build.gradle

@@ -7,13 +7,13 @@ buildscript {
                 compileSdkVersion: 31,
                 targetSdkVersion: 31
         ]
-        androidGradlePluginVersion = '3.6.2'
-        googleServicesGradlePluginVersion = '4.3.2'
+        androidGradlePluginVersion = '7.0.4'
+        googleServicesGradlePluginVersion = '4.3.10'
         huaweiAgconnectVersion = '1.2.1.301'
         huaweiHMSPushVersion = '5.3.0.304'
         huaweiHMSLocationVersion = '4.0.0.300'
         kotlinVersion = '1.4.32'
-        onesignalGradlePluginVersion = '[0.12.6, 0.99.99]'
+        onesignalGradlePluginVersion = '[0.14.0, 0.99.99]'
     }
 
     repositories {

OneSignalSDK/onesignal/build.gradle

@@ -26,6 +26,12 @@ android {
             minifyEnabled false
         }
     }
+
+    // Forced downgrade to Java 8 so SDK is backwards compatible in consuming projects
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
 }
 
 // api || implementation = compile and runtime