FlagBagType support

[michnovka]

This is initial commit for FlagBagType support.

Lets discuss in here

[michnovka]

I have ported also BitmaskToBitFlagsValueTransformer, but I dont think this is going to be used now. In fact the whole as_value part makes little to no sense for me under the new implementation. One of the issues is that the new 2.x EnumType extends the Symfony's own EnumType and not the ChoiceType which was the case with 1.x version. So if we use DataTransformer that spits out int and not BackedEnum[], then the Symfony EnumType does not handle it and fails.

I have made BitmaskToBitFlagsValueTransformerTest so I think we can keep the DataTransformer in the package, maybe somebody will find it useful. But Id remove the as_value option from the FlagBagType and would only allow it to work with the FlagBagToCollectionTransformer (refactored version of SingleToCollectionFlagEnumTransformer)

WDYT @ogizanagi ?

[ogizanagi]

I have ported also BitmaskToBitFlagsValueTransformer, but I dont think this is going to be used now. In fact the whole as_value part makes little to no sense for me under the new implementation.

I agree, let's remove this part until it is proven useful.
I don't want to strictly port every 1.x features as is, only what makes sense regarding the new PHP 8.1 native enums implementation. Also we don't need everything to land in 2.0.0, just what can impact the design and main interfaces.

[michnovka]

Also we don't need everything to land in 2.0.0, just what can impact the design and main interfaces.

Yes, but I would like to include SQL enum, this PR and also FlagBag DBAL type for sure

[michnovka]

This is ready for merge @ogizanagi

[michnovka]

One important note: I have made the FlagBag::getBitmask() public. I think its a useful tool to be used with FlagBags and dont see any reason why it should stay protected.

[michnovka]

@ogizanagi changes committed, ready for merge

[ogizanagi]

Thanks @michnovka for working on this feature, this is much appreciated.

[michnovka]

@ogizanagi np, I use this lib so I like to contribute. I will see if I can work on FlagBag DBAL type when #182 is merged