Re-add support for implode, substr and json_encode about smarty HOT 3 CLOSED

There is a problem with implode. Using implode (or join) as a modifier in templates (prior to Smarty v5) (on PHP8), has to be done as follows: <td class="{' '|implode:$classes|escape}">, since passing the separator after the array is no longer supported in PHP.

As a modifier, this seems silly. It would be more intuitive to flip the arguments, in the way Twig does it: {{ [1, 2, 3]|join('|') }}. But we cannot just flip the arguments. We could detect argument types and throw a deprecation warning.

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It seems Smarty v5 also supports strlen, time, count, is_array and in_array as functions. (They are implemented as FunctionHandlers.) This is undocumented.

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Smarty also supports explode. It's undocumented, but it has been in the unit tests. However, the parameter order is weird and we cannot auto-fix it, since both parameters are strings. I propose to deprecate explode and promote split with the parameters reversed.
For consistency, this would also mean we should implement join in favor of implode.

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