Add RFC: Codec Identifiers

[derrod]

Description

This RFC intends to facilitate discussion to find a way to move away from storing codec identifiers as strings. This is to avoid string comparisons and remove some redundancies such as outputs defining their own codec enumerations.

Motivation and Context

String comparisons are slow, error prone (case sensitivity, typos, etc.), and generally ugly. Most outputs convert from strings to internal enumerations anyway which could be made redundant by providing them in the first place.

Link to RFC