Flutter templates example app Gradle memory settings (flutter#156201)

Adding even more memory to see if it addresses flakes:

* flutter#156063 (comment)

Author: dcharkes

packages/flutter_tools/templates/app_shared/android.tmpl/gradle.properties.tmpl

@@ -1,3 +1,3 @@
-org.gradle.jvmargs=-Xmx4G -XX:MaxMetaspaceSize=2G -XX:+HeapDumpOnOutOfMemoryError
+org.gradle.jvmargs=-Xmx8G -XX:MaxMetaspaceSize=4G -XX:ReservedCodeCacheSize=512m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
 android.enableJetifier=true

packages/flutter_tools/templates/module/android/gradle/gradle.properties.tmpl

@@ -1,3 +1,3 @@
-org.gradle.jvmargs=-Xmx4G -XX:MaxMetaspaceSize=2G -XX:+HeapDumpOnOutOfMemoryError
+org.gradle.jvmargs=-Xmx8G -XX:MaxMetaspaceSize=4G -XX:ReservedCodeCacheSize=512m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
 android.enableJetifier=true