By moving `Certificate` to `LibCrypto` it is possible to reuse a bunch
of code from in `LibCrypto` itself. It also moves some constants
and pieces of code to a more appropriate place than `LibTLS`.
This also makes future work on WebCryptoAPI easier.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
This gets rid of a couple FIXMEs and allows reusing the logic of
validating this field between different algorithms. While we're here,
expand its logic to match the constraints as outlined in RFC 7517.
