Fix BufferSource algorithms for shared and resizable buffers

[MattiasBuelens]

Previously, many BufferSource algorithms were using internal slots such as [[ByteOffset]] and [[ByteLength]] directly. However, with the addition of SharedArrayBuffer (#353, #1311) and [AllowResizable] (#982), this comes with extra caveats:

• To get the byte length of a SharedArrayBuffer, we need to use ArrayBufferByteLength to match SharedArrayBuffer.prototype.byteLength.
• To get the byte length of a "length-tracking" typed array, we need to use TypedArrayByteLength. Similarly, for a length-tracking DataView, we need to use GetViewByteLength.
• To get the byte offset of a typed array or DataView, we first need to check if the view is still inbounds using IsArrayBufferViewOutOfBounds.

Transferring an ArrayBuffer must also take into account whether it should remain resizable or not. Fortunately, we can use the new ArrayBufferCopyAndDetach operation for that.

• I added an optional preserveResizability parameter to "transfer an ArrayBuffer", so specifications can choose whether to preserve resizability or not. By default, this is not preserved. (Most specs aren't using [AllowResizable] yet anyway.)
• I removed the realm parameter of that algorithm, since ArrayBufferCopyAndDetach doesn't accept such a parameter. According to WebDex, no specs were actually using that parameter anyway.

Open questions:

• When dealing with views backed by a SharedArrayBuffer, what memory ordering should we use? ECMAScript seems to use SEQ-CST pretty much everywhere (e.g. %TypedArray%.prototype.byteLength), but "get a copy of the bytes" uses UNORDERED for GetValueFromBuffer.

Fixes #1312.
Fixes #1385.

• At least two implementers are interested (and none opposed):
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• Tests are written and can be reviewed and commented upon at:
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• Implementation bugs are filed:
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  • webidl2.js: …
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(See WHATWG Working Mode: Changes for more details.)

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