scripts: Reference script templates from other script templates

[RaniAgus]

It would be great if we were able to write this:

script mul(a int, b int) {
  return a * b;
}

script double(num int) {
  return @mul(num, 2);
}

And map the function call to the correct script template like this:

<script type="text/javascript">function __templ_mul_5a85(a, b){return a * b;}</script>
<script type="text/javascript">function __templ_double_5a85(num){return __templ_mul_5a85(num, 2);}</script>

So we could reuse logic from both client and server sides.