Feature: #88907 - Always enable filter in SelectMultipleSideBySide fields

See Issue #88907

Description

The filter functionality of fields type = select with renderType = selectMultipleSideBySide is always enabled now.

Impact

Before:

Now just omit the line 'enableMultiSelectFilterTextfield' => true, the behaviour will stay the same.

A migration wizard is available that removes the option from your TCA and leaves a message where code adaption has to take place.