Streamlines a common middleware pattern and provides foundations for avoiding variably sized v8::ExternalReferences & enabling fully monomorphic op callpaths
`handleWasmStreaming` is the function that provides the binding with
the `fetch` API needed for `WebAssembly.instantiateStreaming()` and
`WebAssembly.compileStreaming()`. When I implemented it in #11200, I
thought V8 was calling these functions with the argument of the
`WebAssembly` streaming functions, without doing any resolving, and so
`handleWasmStreaming` awaits for the parameter to resolve. However,
as discovered in
https://github.com/denoland/deno/issues/13917#issuecomment-1065805565,
V8 does in fact resolve the parameter if it's a promise (and handles
rejections arising from that).
This change removes the `async` IIFE inside `handleWasmStreaming`,
letting initial errors be handled synchronously (which will however
not throw synchronously from the `WebAssembly` namespace functions).
Awaiting is still necessary for reading the bytes of the response,
though, and so there is an `async` IIFE for that.
This note about how `v8::SnapshotCreator::create_blob` must not be
called from a `HandleScope` stopped being relevant in #6801, and was
now attached to code that had nothing to do with `HandleScope`s.
When an exception is thrown during the processing of streaming WebAssembly,
`op_wasm_streaming_abort` is called. This op calls into V8, which synchronously
rejects the promise and calls into the promise rejection handler, if applicable.
But calling an op borrows the isolate's `JsRuntimeState` for the duration of the
op, which means it is borrowed when V8 calls into `promise_reject_callback`,
which tries to borrow it again, panicking.
This change changes `op_wasm_streaming_abort` from an op to a binding
(`Deno.core.abortWasmStreaming`). Although that binding must borrow the
`JsRuntimeState` in order to access the `WasmStreamingResource` stored in the
`OpTable`, it also takes ownership of that `WasmStreamingResource` instance,
which means it can drop any borrows of the `JsRuntimeState` before calling into
V8.
