Add gradle option to allow/show System.out.print logs (flutter/engine#38104)

This is useful for java test debugging.
Audit of all java tests shows only 4 logged lines so this should
not add log spam but will aid in contributor test debugging.

engine/src/flutter/shell/platform/android/test_runner/build.gradle

@@ -57,6 +57,7 @@ android {
         events "passed", "skipped", "failed", "standardOut", "standardError"
         exceptionFormat "full"
         showStackTraces true
+        showStandardStreams true
       }
     }
   }