Parse JSON floating point literals properly,
No longer throwing a SyntaxError when the decimal portion
of the number exceeds the capacity of u32.
Added tests to AK/TestJSON and LibJS/builtins/JSON/JSON.parse
The current implementation of step 2a sort of manually implemented GetV
with a ToObject + Get combo. But in the call to Get, the receiver wasn't
the correct object. So when invoking toJSON, the receiver was an Object
type rather than a BigInt.
This also adds spec comments to SerializeJSONProperty.
