[BigInt tests][No merge] ❌🐰 Apple

[LiarPrincess]

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Please read the #242 Using tests from “Violet - Python VM written in Swift” before.

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=== DO NOT MERGE! Discussion only. ===

🐰 Discussion

Tests copied and adapted from: github.com/apple/swift/test/Prototypes/BigInt.swift.

This is more of a "Is there anything interesting in there?", rather than "Let's use those tests.". If you see something, then we may want to move it to appropriate location.

Not sure about license… technically this is github.com/apple/swift, so who cares… but somebody may want to look into this.

❌ Failures

Div, xor and magnitude.

Nothing interesting, they were described in other PRs.