Spec needs to document 'this'-parameters for functions

[DanielRosenwasser]

#6018

[DanielRosenwasser]

Relevant: relationships need to be updated

if M has a this-parameter whose type is not the void type, then it must be a subtype of the this-parameter type of N or N must not have a this-parameter.

if M has a this-parameter whose type is not the void type, then it must be assignable to the this-parameter type of N or N must not have a this-parameter.

if M has a this-parameter whose type is not the void type, then it must be comparable to the this-parameter type of N or N must not have a this-parameter.