Implement schema-aware diffing for detail diff

[t0yv0]

The task is to build an algo that compares prior and planned state at Pulumi level.

Resolves #1895
Resolves #186
Resolves #1504

func makePulumiDetailedDiff(
	ctx context.Context,
	tfs shim.SchemaMap,
	ps map[string]*SchemaInfo,
	oldState, plannedState resource.PropertyMap,
) (map[string]*pulumirpc.PropertyDiff) {

This is intended to replace the current signature that tries to do inference on the shim.InstanceDiff object that wraps the terraform.InstanceDiff object:

func makeDetailedDiff(
	ctx context.Context,
	tfs shim.SchemaMap,
	ps map[string]*SchemaInfo,
	olds, news resource.PropertyMap,
	tfDiff shim.InstanceDiff,
) (map[string]*pulumirpc.PropertyDiff, pulumirpc.DiffResponse_DiffChanges) {

As TF CLI does not access terraform.InstanceDiff but renders diffs by comparing existing and planned state, this would make bridged providers behave more in line with TF expected behavior.

The schema-aware requirement comes down to keep tracking schema (SchemaInfo/SchemaMap) or else current paths through the transformation. When diffing collections, the algo needs to be able to tell when the two diffed PropertyValue arrays are representing a TF set under the hood. PropertyPathToSchemaPath and LookupSchemas can be helpful here.

#2200 outlines a suggestion for how set collection diffs should be handled. The cases where plannedState has unknowns with sets are a bit under-specified, suggest treating the entire new set as an unknown in that case old => UNKNOWN.

This change should be flagged together with all the other work in the epic for a consistent rollout.