Add :encode and :decode modifiers

https://docs.expressionengine.com/latest/templates/variable_modifiers.html

It would be nice if we had a base64_encode/decode modifiers on variables. In some cases html needs to be passed as an embed variable, but it gets totally clobbered/confused when quotes are in an embed variable.

Specifically when used in embeds:

{embed="some/template" var="foo <a href="#">bar</a>" encode="yes"}

Or

{embed="some/template" var="{something:encode}"}

Then on the output

{embed:foo:decode}

Generally having :encode or :decode could be helpful.