Add isSubtype function for runtime values

[dsainati1]

Closes #473

Description

Adds a fun isSubtype(of otherType : Type) : Bool to runtime types which compares their static types and returns true if the receiver is a subtype of the argument and false if not. Note that unknown types (which have no static type) will return false if they are the receiver of the method or the argument, as it is illogical to check whether an unknown type is a supertype or subtype of anything else.

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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

[codecov-commenter]

Codecov Report

Merging #1189 (863598e) into master (01ae3c2) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1189      +/-   ##
==========================================
+ Coverage   73.38%   73.39%   +0.01%     
==========================================
  Files         272      272              
  Lines       34584    34603      +19     
==========================================
+ Hits        25379    25398      +19     
  Misses       8032     8032              
  Partials     1173     1173              

Flag	Coverage Δ
unittests	73.39% <100.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
runtime/interpreter/value.go	79.13% <100.00%> (+0.06%)	⬆️
runtime/sema/meta_type.go	100.00% <100.00%> (ø)

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[turbolent]

Nice work!

[SupunS]

LGTM!

[turbolent]

Great work on your first PR! 👏 🥳