Resolve remaining issues from bugzilla

[ ] Using platform object example
[ ] consider allowing non-matching enums to be converted to a particular value
[ ] Support subclassing Array
[ ] allow attributes to have different types for their getter and setter
[ ] Function's length property is inconsistent with EcmaScript
[ ] "a value (matching DefaultValue)"
[ ] freeze/seal/preventExtensions should throw for Nodes (and maybe any WebIDL interface)
[ ] "optional any" is nonsense that should be disallowed
[ ] "The return type of the operation is given by th..."
[ ] enum should be able to inherit from another enum
[ ] Why do we disallow overloading across partial interfaces?
[x] Stop using "octet" now #843
[ ] Fixed length sequences of varying types
[ ] " The result of converting an IDL value of any b..."
[ ] "Prose accompanying an interface with a pair ite..."
[ ] factor out "location of properties that usually go on an interface prototype object" wording
[ ] Require that promise rejection are instances of error
[ ] Remove requirement for prose around iterable<> if object has indexed properties
[x] Allow partial enums -- https://github.com/heycam/webidl/issues/184
[ ] Define context variables, such as "context object"
[ ] Data properties
[x] Define [LegacyNewObject]
[ ] Support holes or undefined values in the sequences as return values?
[ ] Inherited method name conflicts with consequential maplike/setlike interfaces should fail
[ ] Should probably perform security checks on arguments too, not just this values
[ ] Make BufferSource more convenient to use
[ ] [EnforceRange] accepts an odd set of input values
[ ] iterable declaration and forEach ECMAScript binding issues
[ ] FrozenArray only provides shallow immutability
[x] Provide text guidance for rejecting promises

whatwg / webidl

Resolve remaining issues from bugzilla #777