POC: Add template forEach function and change it to forEach implementation

[korzio]

As a djv validator developer
I want to have a template forEach function to easily construct cicles for validator functions

Example:
Instead of

tpl('for ($1; $2 < $3.length; $2++) {', tpl.cache('0'), tpl.cache('0'), tpl.data);
  tpl.data.push(`[${tpl.cache('0')}]`);

  const condition = `...`;
  const error = `...`;

  tpl(`if (${condition}) ${error}`, tpl.data);
  tpl.data.pop();

I want smth like

tpl.forEach(tpl.data, () => condition, () => error) // or even map