Add generics to WithMapping

[joelharkes]

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1️⃣ Why should it be added? What are the benefits of this change?

Adding more typesaftey and benefit of static analyzer.

Before:

After

/**
 * @implements WithMapping<MyModel>
*/
class MyExport {
    public function map($row){
       // IDE Knows the right type now = MyModel.
   }
}

2️⃣ Does it contain multiple, unrelated changes? Please separate the PRs out.

No i just started by adding type safety to WithMapping, i could add it for all FromX iterfaces as well but i wouldnt want to make it too big at once.
First i would like to check if you like this before i added generic types everywhere.

3️⃣ Does it include tests, if possible?

No it's just doctype

4️⃣ Any drawbacks? Possible breaking changes?

No breaking changes, no effect on any existing code, even static analyzer with by default assume mixed type.

5️⃣ Mark the following tasks as done:

• Checked the codebase to ensure that your feature doesn't already exist.
• Take note of the contributing guidelines.
• Checked the pull requests to ensure that another person hasn't already submitted a fix.
• Added tests to ensure against regression. => No testing needed i think?

6️⃣ Thanks for contributing! 🙌

🥳

[patrickbrouwers]

Love this, thanks!

Which other concerns you have in mind that are relevant for generics? I wouldn't mind if you add some more to this PR.

[joelharkes]

FromQuery => can be type generic based on Builder
FromCollection / FromArray / FromIterator

All the ToX interfaces as well.

I prefer merging this first as this is the most problematic for Lara/PHPStan.
and make a separate PR for the others