Encode value when an array

[stutteringp0et]

This adjustment allows complex field types (types with more than one input) to store and retrieve data.

Summary of Changes

Test value before save, if it's an array, json encode it

Testing Instructions

Hard to say without installing a 3rd party custom field plugin

Expected result

it should be transparent

Actual result

transparent on my end

Documentation Changes Required

none

[mbabker]

Duplicate of #19025 (if that PR is accepted eventually things will merge up into 4.0, no need to submit the same fix against both versions as long as we are still branch merging).