Update browser support caveats

[AminArria]

Most of the caveats can be removed:

• Edge 79+ supports TextEncoder and TextDecoder APIs (https://caniuse.com/textencoder)
• Edge 79+ and Safari 14+ supports BigInt (https://caniuse.com/bigint)

[alexcrichton]

Thanks! Instead of deleting the sections though could they perhaps be re-worded? Something along the lines of "browsers before X" need consideration?

[AminArria]

@alexcrichton made the changes, let me know if the wording is fine or it needs some more tweaking

[alexcrichton]

Thanks!

[tash-2s]

I think Safari 14+ isn't still supported. It has BigInt but doesn't have BigUint64Array.

ReferenceError: Can't find variable: BigUint64Array

https://caniuse.com/?search=BigUint64Array
https://bugs.webkit.org/show_bug.cgi?id=190800

[Firaenix]

Can also confirm BigUint64Array does not work on Safari.

I do believe there is potential for this to be polyfilled however.
We would need to amend the existing u64 polyfill.