[BC BREAK] PHPStan improvements

[kbond]

Note

This is only a BC break for static analysis.

Since 90+% of the time, you don't really care about the key when using Collection, I've swapped the @template for these two values and used PHPStan's default template type (as array-key) for the key:

Before:

@return Collection<array-key,object>

After:

@return Collection<object>

If you still want to define the key, it's the second template:

@return Collection<object,int>