Wording: refine "object" links, define platform operand/operator

The default linking for [=object=] is to FileAPI's blob URL entry
object member[1], which is definitely wrong.

Replace such references with:

* Infra's ordered map[2], when a dictionary is intended, as that's
  what a JavaScript object is translated into via bindings.

* Links to new definitions for "platform operator" and "platform
  operand" which include the "implementation-defined" phrase so links
  to the terms can be greatly simplified. These definitions should
  be further expanded to include "connect", "input" and "output" but
  that can be tackled later.

This reduces the number of "implementation-defined" phrases to just
a handful in the spec, which helps with #462.

[1] https://www.w3.org/TR/FileAPI/#blob-url-entry-object

[2] https://infra.spec.whatwg.org/#ordered-map

Co-authored-by: Anssi Kostiainen <[email protected]>
Co-authored-by: Ningxin Hu <[email protected]>