Propose to add the possibility to set a fieldset-specific renderer to the fieldset elements

Look at the \Magento\Framework\Data\Form\Element\Fieldset::addField method:

As you can see a fieldset tries to set a common renderer to an element:

It is good, but I propose to do it better: additionally try to set a renderer, specific to the fieldset, if it is present, for example:

if ($renderer = $this->getElementRenderer()) {