Re: [whatwg/webidl] Fix `BufferSource` algorithms for shared and resizable buffers (PR #1529)

@MattiasBuelens commented on this pull request.

Quick self-review.

>  <div algorithm>
     The <dfn export for="BufferSource">byte length</dfn> of a [=buffer source type=] instance
     |bufferSource| is the value returned by the following steps:
 
     1.  Let |jsBufferSource| be the result of [=converted to a JavaScript value|converting=]
         |bufferSource| to a JavaScript value.
-    1.  If |jsBufferSource| has a \[[ViewedArrayBuffer]] internal slot, then return
-        |jsBufferSource|.\[[ByteLength]].
-    1.  Return |jsBufferSource|.\[[ArrayBufferByteLength]].
+    1.  If |jsBufferSource| has a \[[ViewedArrayBuffer]] [=/internal slot=]:
+        1.  If |jsBufferSource| has a \[[TypedArrayName]] [=/internal slot=]:
+            1.  [=/Assert=]: |jsBufferSource| is a [=typed array type=] instance.
+            1.  Let |taRecord| be [$MakeTypedArrayWithBufferWitnessRecord$](|jsBufferSource|,
+                Seq-Cst).
+            1.  Return [$TypedArrayByteLength$](|taRecord|).

[TypedArrayByteLength](https://tc39.es/ecma262/multipage/ordinary-and-exotic-objects-behaviours.html#sec-typedarraybytelength) asserts that [IsTypedArrayOutOfBounds(taRecord)](https://tc39.es/ecma262/multipage/ordinary-and-exotic-objects-behaviours.html#sec-istypedarrayoutofbounds) is false, which we didn't explicitly check. We should check for that, to align with [%TypedArray%.prototype.byteLength](https://tc39.es/ecma262/multipage/indexed-collections.html#sec-get-%typedarray%.prototype.bytelength).


```suggestion
            1.  If [$IsTypedArrayOutOfBounds$](|taRecord|) is true, return 0.
            1.  Return [$TypedArrayByteLength$](|taRecord|).
```

> +    1.  Otherwise, if [$IsSharedArrayBuffer$](|jsBufferSource|) is true:
+        1.  [=/Assert=]: |jsBufferSource| is a {{SharedArrayBuffer}}.
+        1.  Return [$ArrayBufferByteLength$](|jsBufferSource|, Seq-Cst).
+    1.  Otherwise:
+        1.  [=/Assert=]: |jsBufferSource| is an {{ArrayBuffer}}.
+        1.  Return |jsBufferSource|.\[[ArrayBufferByteLength]].

[ArrayBufferByteLength](https://tc39.es/ecma262/multipage/structured-data.html#sec-arraybufferbytelength) supports both `ArrayBuffer` and `SharedArrayBuffer`, so we can combine these steps.

```suggestion
    1.  Otherwise:
        1.  [=/Assert=]: |jsBufferSource| is an {{ArrayBuffer}} or a {{SharedArrayBuffer}}.
        1.  Return [$ArrayBufferByteLength$](|jsBufferSource|, Seq-Cst).
```

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