Add a shared number conversion layer backed by double-conversion and route
Number(), parseFloat(), numeric literal parsing, and Number formatting through
it. This fixes decimal precision/rounding edge cases, validates malformed
decimal literals such as missing exponent digits, and handles JS string-number
parsing rules more consistently.

Add parser/compiler/runtime support for throw expressions, using and await using
declarations, disposal stacks, dispose symbols, and SuppressedError handling.
Wire disposal cleanup through blocks, returns, breaks, continues, and for-of
loops, including async disposal paths and suppressed errors.

Also add DisposableStack and AsyncDisposableStack builtins, AsyncIterator helper
plumbing, and focused tests/spec coverage for resource management, suppression,
throw expressions, and async iterators.

- give Object.getOwnPropertyDescriptors result objects a normal Object prototype
- add SharedArrayBuffer @@species and prototype byteLength support
- stop exposing async functions as constructors with own prototype properties
- expose AsyncFunction through Symbol.toStringTag
- reject async/function line terminator parsing
- reject await in async function parameter initializers

900% increase in throughput