Generally IDL objects have been 1:1 with ECMAScript objects, except for
SharedArrayBuffer. That was instead represented as
[AllowShared] ArrayBuffer, although that includes ArrayBuffer as well.
This created a number of challenges, e.g., how to return a
SharedArrayBuffer object.

So we make these changes here that will also require corresponding
downstream fixes:

* SharedArrayBuffer is now its own type.
* [AllowShared] only applies to buffer view types.
* AllowSharedBufferSource takes over from [AllowShared] BufferSource.

Fixes #865 and fixes #961.

- Turn the table into a proper table instead of using <br>.
- Attempt to link ECMAScript for certain ArrayBuffer/SharedArrayBuffer references.
- Use typedefs for the buffer source type algorithms again and don't change the for attribute (mostly).
- Drop the IsSharedArrayBuffer asserts when we already (implicitly) assert it's an ArrayBuffer.