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.
- Document the above in coding conventions.

SpecCodingConventions.md

@@ -76,6 +76,7 @@ Example:
 * Bikeshed will automatically style linked terms appropriately, for example Web IDL types show up as `code`. Try to avoid manual styling wherever possible; if you're not getting the style you expect, you may have incorrect definitions or links.
 * Outside of examples, which should be appropriately styled automatically, literals such as numbers within spec prose are not JavaScript values and should not be styled as code.
 * Strings used internally (e.g. operator names) should not be styled as code.
+* When concisely defining a list's members or a tensor's layout, use the syntax `*[ ... ]*` (e.g. _"nchw" means the input tensor has the layout *[batches, inputChannels, height, width]*_)
 
 
 ### Algorithms