feat(mapper): support union types in docblocks

[aazsamir]

This pull request adds support for union types along with partially-understanding types defined in docblock.

class StoreRequest {
    /** @var string|string[] */
    public string|array $tags;
}

mixed type is also supported

class StoreRequest {
    /** @var string|mixed[] */
    public string|array $tags;
}

This means that it is now also supported.

class StoreRequest {
    /** $var string[] */
    public array $tags;
}

There are still a few edge cases to resolve, but I would say this is MVP.

[brendt]

Looks promising!

[brendt]

@aazsamir I'm sorry for being very late reviewing this PR :( Because of that, there's now a new feature (in 3.x) that has quiet the impact on this PR: #1791

Unfortunately I won't be able to merge this unless it's being refactored and targeted towards 3.x. Sorry for not getting to this earlier, I really appreciate the effort you put into it!

Let me know if I can be of any help.