Wording change: Dedupe dictionary member type and default definitions

Bikeshed automatically annotates dictionary members with types and
defaults, so repeating that in the prose is extra work and extra
noise. Remove both and reword as needed. For #483

Also:

- Simplify text by removing "Specifies" from most definition prose.
- Replace "sequence" with "list" in prose.
- Consistently give list member definitions using *[ ... *] styling.

TODO: Add the above to SpecCodingConventions.md