Formalise rules around create methods

[IsakNaslundBh]

Description:

The create methods needs some level of compliance. The initial state was that they:

• Need to sit in a file or folder matching the return type (this is fine)
• Need to have a method name matching the file name (this has proven not fine, and is being turned off in Exclude create methods from method name must contain file name #529

Simply removing the separate check, without any additional guidance might be a bit to relaxed.

Could for example be that create methods must live in a file that is either matching file name or matching return type.

Happy for other suggestions though.