Fixed $model->countRelated() failing when the relation is reusable

[zsilbi]

Hello!

• Type: bug fix

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Small description of change:

The uniqueKey used to store reusable related records in ModelsManager is currently generated only from the conditions used to lookup the records.

For example:
It uses the same key for $robot->getParts(["some" = "thing"]) and $robot->countParts(["some" = "thing"]).
If the related records are accessed again using a different method, it will return the result of the first.
In this case, it will be a Resultset instead of an integer.

I added the retrieveMethod variable to the uniqueKey generation.
Added some tests for Model::__call()

Thanks,
zsilbi

[zsilbi]

@sergeyklay I'd also change Model::__callStatic() to throw an exception if the method is unknown, like Model::__call() does.

What do you think?

[sergeyklay]

@zsilbi Let's use a separated PR to change Model::__callStatic()

[codecov]

Codecov Report

Merging #14444 into 4.0.x will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            4.0.x   #14444      +/-   ##
==========================================
+ Coverage   67.67%   67.68%   +0.01%     
==========================================
  Files         482      482              
  Lines      111229   111235       +6     
==========================================
+ Hits        75275    75294      +19     
+ Misses      35954    35941      -13

[niden]

Thank you @zsilbi