`isHexChecksumAddress` is poorly named and documented

[davidmurdoch]

https://github.com/MetaMask/utils/blob/1bea7f378c37117260912af1921556bc57110d20/src/hex.ts#L63-L71

This function does NOT return if the given string is a "valid hex checksum address" (or a "Hex Checksum Address"). It returns true if the characters used in the given string are all allowed in an checksummed address.

The function (and likely some other similarly confusing functions/docs in this same file) should be updated to reflect their purpose.

[mcmire]

@davidmurdoch I agree, this is a confusing function. Not only does it not tell you whether you have a truly valid checksum address, we're running a string against a pattern ostensibly so we can reliably convert it into a more useful type — except all we can tell TypeScript is that it's a string that starts with 0x, which is better than nothing, but still not that useful. We should investigate how we are using this function in practice and figure out whether this is the right thing to use.