Explicitly specify --api-overloaded-method-order source for metalava

Previously, `--api-overloaded-method-order source` was the default if
that option was not specified but the other change in this topic is
switching it to `--api-overloaded-method-order signature` to match the
behavior in AndroidX. This change explicitly specifies the option
needed by Soong's use of metalava.

Bug: 285140653
Test: m checkapi
Change-Id: I00e049e0d991e650ab9940a3d495ed2b6e7480f8

java/droidstubs.go

@@ -539,6 +539,10 @@ func metalavaCmd(ctx android.ModuleContext, rule *android.RuleBuilder, javaVersi
 	// See b/285140653 for more information.
 	cmd.FlagWithArg("--api-class-resolution ", "api")
 
+	// Force metalava to sort overloaded methods by their order in the source code.
+	// See b/285312164 for more information.
+	cmd.FlagWithArg("--api-overloaded-method-order ", "source")
+
 	return cmd
 }