[charcoal/admin] Add support for dynamic type field to ObjectContainerTrait

[mcaskill]

This would improve support for polymorphic model relationships, similar to CollectionContainerTrait.

This would probably require a dedicated model loader that also resolves. Alternatively, just use a collection loader.

charcoal/packages/admin/src/Charcoal/Admin/Ui/ObjectContainerTrait.php

Lines 88 to 117 in c72eca8

	/**
	* Set the object type.
	*
	* @param string $objType The object type.
	* @throws InvalidArgumentException If provided argument is not of type 'string'.
	* @return ObjectContainerInterface Chainable
	*/
	public function setObjType($objType)
	{
	if (!is_string($objType)) {
	throw new InvalidArgumentException(sprintf(
	'Object type must be a string, received %s.',
	(is_object($objType) ? get_class($objType) : gettype($objType))
	));
	}
	$this->objType = str_replace(['.', '_'], '/', $objType);
	return $this;
	}
	/**
	* Retrieve the object type.
	*
	* @return string|null
	*/
	public function objType()
	{
	return $this->objType;
	}