Reexamine where we convert from Terraform values into `attr.Value`s.

[paddycarver]

Currently, the framework is following a model of keeping everything as a tftypes.Value all the way through the framework, until the config, state, or plan tries to retrieve it, then converts back from an attr.Value into a tftypes.Value when setting the config, state, or plan. That means that for all the framework code, we're more likely to be using the tftypes.Value abstraction than the attr.Value abstraction provider developers are using and expect.

I'm suspicious that we can clean up a lot of code, handle a lot of edge cases, and make more things work intuitively the way provider developers expect if we instead convert from tftypes.Values into attr.Values when handling protocol requests, and then passing around the attr.Values.

[bflad]

I think this pairs well with #215 👍

[bflad]

Created bespoke issues for tracking specific pieces of framework updates:

• attr: Remove Requirement for tftypes Handling from Exported Type/Value Interfaces #588
• attr/xattr: Consider Deprecating tftypes.Value Handling In Preference of attr.Value Handling #589
• Consider Surfacing Framework Type System Data for Config/Plan/State #590

If there are other places which need updates, we can create other new issues.