wit: add Stability.Versioned method

Author: ydnar

wit/stability.go

@@ -8,6 +8,7 @@ import (
 type Stability interface {
 	Node
 	isStability()
+	Versioned() bool
 }
 
 // _stability is an embeddable type that conforms to the [Stability] interface.
@@ -24,9 +25,19 @@ type Stable struct {
 	Deprecated *semver.Version
 }
 
+// Versioned always returns true for [Stable].
+func (*Stable) Versioned() bool {
+	return true
+}
+
 // Unstable represents an unstable WIT feature defined by name.
 type Unstable struct {
 	_stability
 	Feature    string
 	Deprecated *semver.Version
 }
+
+// Versioned returns whether [Unstable] is deprecated.
+func (u *Unstable) Versioned() bool {
+	return u.Deprecated != nil
+}