Allow using a static method as a resolver

[illia-v]

Description

In a project I had to define a resolver that gets some data from the root argument.
It was not possible to use self because of some mypy warnings. Therefore, I wanted to remove the self argument.
It was possible to remove it without using @staticmethod, but mypy complained that Self argument missing for a non-static method (or an invalid type for self).

So, I had to add @staticmethod.
I tried adding it before @strawberry.field, but Python did not add the field to __dataclass_fields__ and a type was not created correctly.
Then, I tried adding it after @strawberry.field, but Strawberry did not like that because AttributeError: 'staticmethod' object has no attribute '__annotations__'. The changes fix this problem.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Documentation

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[botberry]

Thanks for adding the RELEASE.md file!

Here's a preview of the changelog:

---

This release fixes an issue that prevented using classmethods and staticmethods as resolvers

import strawberry

@strawberry.type
class Query:
    @strawberry.field
    @staticmethod
    def static_text() -> str:
        return "Strawberry"

    @strawberry.field
    @classmethod
    def class_name(cls) -> str:
        return cls.__name__

---

Here's the preview release card for twitter:

Here's the tweet text:

🆕 Release (next) is out! Thanks to Illia Volochii for the PR 👏

Get it here 👉 https://github.com/strawberry-graphql/strawberry/releases/tag/(next)

[codecov]

Codecov Report

Merging #1430 (d2a93d2) into main (ab4a6a6) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1430      +/-   ##
==========================================
- Coverage   98.08%   98.08%   -0.01%     
==========================================
  Files         119      121       +2     
  Lines        4129     4228      +99     
  Branches      599      710     +111     
==========================================
+ Hits         4050     4147      +97     
  Misses         42       42              
- Partials       37       39       +2     

[BryceBeagle]

I have a more robust fix for this that also supports classmethods working right now 👍. Just need to get mypy checks to comply. Hopefully we can get this merged by tonight

[BryceBeagle]

After much deep-diving into (and frustration with!) the underlying mechanics of staticmethod and classmethod binding, I think this solution should be very robust and satisfy most, if not all, edge cases. I took the liberty of committing to your branch @illia-v.

This should be ready for review @patrick91. Let me know if I should add any more comments/documentation anywhere.

[botberry]

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