[#53334909] Upgrade handlebars_assets

* Apparently, if you pass a function into a template,
you can no longer send it arguments eg {{myFunction arg1 arg2}}.
Changed some tag code to deal with this.

* Changed helpers that expected 'block' to be callable to now
call block.fn

Note that you will probably have to `rake tmp:clear` and restart Chorus
after this commit to fix development mode.