Add setAttributes to ClassGenerator

[jakublabno]

Feature Request

Q	A
New Feature	yes
RFC	no
BC Break	no

Summary

Please add support for attributes generation like it has place for DocBlockGenerator
It should support one attributes or a group of them

#[Attribute1(arg: true)]
#[Attribute2]
class SampleClass implements
{
}

[Ocramius]

Probably requires a dedicated AttributeGenerator: consider sending a patch/proposal.

[jakublabno]

Should I leave compatibility with 7.4?

[Ocramius]

Your pick: PHP 7.4 is almost dead, so you can drop it, if it helps development.

[Ocramius]

See also #143

[jakublabno]

#145