Make DEFFRAME Attributes an identifier-keyed map

[kalzoo]

Currently, the spec defines fixed keys (such as HARDWARE-OBJECT) as attributes of a DEFFRAME. This has some limitations:

• It's a Rigetti-developed and Rigetti-focused set of keys and definitions, when Quil is meant to be agnostic
• Even for Rigetti, it requires a spec change to add or modify these

This PR proposed a change to make this a simple map<identifier, expression | string> allowing for backends to interpret the information however they'd like. That puts the onus on the hardware provider to describe the information that's present within these, but that feels appropriate given the nature and use of frame definitions in Quil.

[stylewarning]

Sorry this took so long for such a simple change. I think this is a good idea.