Fixing build errors in complex programs

[dkcumming]

Currently stable-mir-json will not build complex programs. Using the target of compiling Solana p-token we can try to iron out these issues. This PR has:

• Added Adt and Ref type handling for the RigidTys in get_prov_type
• TODO: Fix string issues with DUMMY_BINDER in formating Fixes Compiler panic on programs using to_string() #27 (rust zulip post in stable mir channel)
• TODO: Fix failure in handling UnevaluatedConst

Returns Ok(None) if we cannot resolve Instance to a specific instance. For example, in a context like this,

fn foo<T: Debug>(t: T) { ... }
trying to resolve Debug::fmt applied to T will yield Ok(None), because we do not know what code ought to run. This > > setting is also affected by the current TypingMode of the environment.

Presuming that coherence and type-check have succeeded, if this method is invoked in a monomorphic context (i.e.,
like during codegen), then it is guaranteed to return Ok(Some(instance)), except for when the instance's inputs hit the > type size limit, in which case it may bail out and return Ok(None).