Fix typos and grammar errors in documentation (#13391)
- Fix 'allows to generate' -> 'allows you to generate' in controlling_generation.md
- Fix 'it's refiner' -> 'its refiner' (possessive) in sdxl.md
- Fix 'it's state' -> 'its state' (possessive) in reusing_seeds.md
- Fix missing word 'you'll a function' -> 'you'll create a function' in sdxl.md
