fix: lenient type checking involving type parameter types

[lars-reimann]

Related to #915

Summary of Changes

As described in #915, the code

fun f<T>(p: (a: T) -> b: String)

pipeline myPipeline {
    // Expected type '(a: T) -> (b: String)' but got '(a: String) -> (result: String)'
    f((a: String) -> a);
}

currently shows an error due to a parameter mismatch (contravariant context). In a covariant context (e.g. for results), however, no such error is shown. That's because when checking whether a type T1 can be assigned to a type T2, we used to replace a type parameter type as T1 with its upper bound (strict) and as T2 with its upper bound (lenient).

We now instead replace a type parameter as T1 with its lower bound (lenient). This simply checks whether there are any substitutions for T1 that could let the subtype relation become true.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ REPOSITORY	git_diff	yes		no	0.09s
✅ TYPESCRIPT	eslint	2	0	0	4.24s
✅ TYPESCRIPT	prettier	2	0	0	1.07s

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (8812944) to head (594d198).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #916   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           92        92           
  Lines        16854     16860    +6     
  Branches      3412      3415    +3     
=========================================
+ Hits         16854     16860    +6     

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[lars-reimann]

🎉 This PR is included in version 0.8.0 🎉

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• npm package (@latest dist-tag)
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