feat(std/testing): add assertInstanceOf

[buttercubz]

Add an assertInstanceOf function for std/testing/asserts.ts

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[bartlomieju]

Is there prior art for such assert? It's the same amount of chars to type as assert(foo instanceof Person) and it seems it's superfluous.

[buttercubz]

@bartlomieju should i change it in the test?

[nayeemrmn]

Duplicate of #5749.

[bartlomieju]

Thanks for the effot @buttercubz but I'm gonna close this PR without merge, as it is a duplicate of already closed PR as pointed by @nayeemrmn. It's always good to open an issue first and discuss before adding new APIs.

[buttercubz]

@bartlomieju
Thank you, I'll have it in mind