Extend subtyping rule for restricted type

[turbolent]

Closes #1479

Description

When checking T <: U{Vs}, we currently require T == U, assuming both are composite values.
However, the latter may actually be a type requirement.

Extend the subtyping check and require T <: U.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[turbolent]

Added another test case which shows that this is not just a problem for references, but an issue with composite dynamic type and restricted static type.

[turbolent]

Added yet another check which shows that this is actually a limitation of the type checker. The dynamic subtype check in the interpreter relies on this check to succeed

[turbolent]

These tests passed the type checking (correctly) and only failed at run-time due to the defensive value transfer check, which in addition to the static check, also checks subtyping for the underlying value.

[codecov-commenter]

Codecov Report

Merging #1480 (29157dc) into v0.23 (bc4ef3f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##            v0.23    #1480   +/-   ##
=======================================
  Coverage   75.98%   75.98%           
=======================================
  Files         283      283           
  Lines       36993    36993           
=======================================
+ Hits        28108    28109    +1     
+ Misses       7612     7611    -1     
  Partials     1273     1273           

Flag	Coverage Δ
unittests	75.98% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/sema/type.go	87.78% <100.00%> (ø)
runtime/sema/simple_type.go	96.29% <0.00%> (+3.70%)	⬆️

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