Editorial: Store and rethrow module instantiation/evaluation errors

This closes #862 by ensuring that repeated calls to ModuleDeclarationInstantiation() and ModuleEvaluation(), for Source Text Module Records, rethrow any exceptions they previously threw, instead of silently succeeding. This clarifies how host environments can do top-down instantiation/evaluation of module graphs, instead of having to do bottom-up instantiation/evaluation in order to record individual failures and thus prevent future instantiation/evaluation.

For background on the trouble caused by the previous approach of silent success, see:

- whatwg/html#1545
- #862
- whatwg/html#2629
- whatwg/html#2595 (comment)

In the process, this helps formalize some of the invariants previously stated in a vague way, such as "ModuleDeclarationInstantiation must have completed successfully", replacing them instead with an explicit [[Status]] field whose contents can be asserted against. It also clarifies the relationship of Module Records that are not Source Text Module Records with respect to these invariants; in brief, they are expected to be leaves in the graph, with no descendants.

Finally, it also updates the machinery involved in module instantiation and evaluation, first by renaming the ModuleDeclarationInstantion() and ModuleEvaluation() abstract methods to Instantiate() and Evaluate(), and also by documenting all of the abstract operations and methods involved. This includes non-normative prose containing example Source Text Module Record graphs and how they are processed.

Closes #916.