Bug 210982 – We need profiling for BigInt math that tells us what format the result of an operation will be

• Status: NEW
• Component: JavaScriptCore

[Saam Barati]

We need to know:
- Will we always produce a BigInt32 (this could happen even when the inputs are HeapBigInt)
- We will always produce a HeapBigInt (this could happen even when the inputs are always BigInt32)
- When we produce both

For example, we'll want some kind of Add on binaryUseKind(BigInt32) that speculates the result doesn't overflow, so it can say it results in BigInt32 definitively

etc.