Sort dependencies when encoding `ResourceInstanceObject`

Resource dependencies are by nature an unordered collection, but they're
persisted to state as a JSON array (in random order). This makes a mess for
`terraform apply -refresh-only`, which sees the new random order as a change
that requires the user to approve a state update.

(As an additional problem on top of that, the user interface for refresh-only
runs doesn't expect to see that as a type of change, so it says "no changes!
would you like to update to reflect these detected changes?")

This commit changes `ResourceInstanceObject.Encode()` to sort the in-memory
slice of dependencies (lexically, by address) before passing it on to be
compared and persisted. This appears to fix the observed UI issues with a
minimum of logic changes.

internal/states/instance_object.go

@@ -1,6 +1,8 @@
 package states
 
 import (
+	"sort"
+
 	"github.com/zclconf/go-cty/cty"
 	ctyjson "github.com/zclconf/go-cty/cty/json"
 
@@ -108,6 +110,13 @@ func (o *ResourceInstanceObject) Encode(ty cty.Type, schemaVersion uint64) (*Res
 		return nil, err
 	}
 
+	// Dependencies are collected and merged in an unordered format (using map
+	// keys as a set), then later changed to a slice (in random ordering) to be
+	// stored in state as an array. To avoid pointless thrashing of state in
+	// refresh-only runs, we can either override comparison of dependency lists
+	// (more desirable, but tricky for Reasons) or just sort when encoding.
+	sort.Slice(o.Dependencies, func(i, j int) bool { return o.Dependencies[i].String() < o.Dependencies[j].String() })
+
 	return &ResourceInstanceObjectSrc{
 		SchemaVersion:       schemaVersion,
 		AttrsJSON:           src,