Use propertyAccessor for BaseFieldDescription::getFieldValue

[VincentLanglet]

It will solve #6795 and we will rely on propertyAccessor implementation instead of a custom one.

We're loosing the parameters option but I'm not sure it's used and it's solvable by using a custom template instead.

Changelog

### Deprecated
- FieldDescription `parameters` option.

[OskarStark]

Do we need property access as composer dep?

[VincentLanglet]

Do we need property access as composer dep?

We already have

[franmomu]

If we use the PropertyAccessor, what about to replace almost everything in getFieldValue?

SonataAdminBundle/src/Admin/BaseFieldDescription.php

Lines 398 to 400 in dbf9e0f

	if ($this->isVirtual() || null === $object) {
	return null;
	}

I think (without trying it) all code below those lines can be replace using PropertyAccessor::getValue

[VincentLanglet]

If we use the PropertyAccessor, what about to replace almost everything in getFieldValue?

SonataAdminBundle/src/Admin/BaseFieldDescription.php

Lines 398 to 400 in dbf9e0f

	if ($this->isVirtual() || null === $object) {
	return null;
	}

I think (without trying it) all code below those lines can be replace using PropertyAccessor::getValue

If I replace everything, I lost the code option then.

[franmomu]

This PR introduces a BC break since code is always set in the current persistence bundles.

[VincentLanglet]

This PR introduces a BC break since code is always set in the current persistence bundles.

@franmomu Do you have a use case ?
The code option should be still supported.

[franmomu]

Apparently it is always like: https://github.com/sonata-project/SonataDoctrineORMAdminBundle/blob/b656ccab02db9abf397e04a69ca0e2bda9bfd455/src/Builder/ListBuilder.php#L127

The problem I guess is that before, code option added a getter option to try to fetch the value, but now if is set and does not exists it only executes: return $object->{$getter}();.

Edit: sonata-project/SonataDoctrineORMAdminBundle#1306

[VincentLanglet]

I made #6855