Iteration and append methods for byte sequence used in standards are undefined

[SuperSonicHub1]

The URL Standard makes use of two byte sequence methods for percent-decoding that go undefined in the Infra Standard:

• iteration and "for each" (used on L409; defined in Infra for lists, sets, and maps)
• appending a byte to a byte sequence (used on L412, L416, 427; defined in Infra for lists and sets)

I believe copy-pasting the existing definitions for lists should be adequate. This brings into question if a byte sequence should be defined as a list of bytes so it can inherit the properties and methods of a list, but that is better left for another issue.

[annevk]

Thanks for raising this. In a way this is a duplicate of #91, but since it's very clear I'm inclined to leave this open for now.

(#110 makes an argument against strings being lists, but maybe byte sequences is still reasonable.)