Export is-editable-element from utils index (#597)

* Export is-editable-element from utils index

* Expose isEditableElement util from utils index

Author: iansan5653

.changeset/nervous-pets-stare.md

@@ -0,0 +1,5 @@
+---
+"@primer/behaviors": patch
+---
+
+Expose `isEditableElement` util

src/utils/index.ts

@@ -1,3 +1,4 @@
 export * from './iterate-focusable-elements.js'
 export * from './unique-id.js'
 export * from './user-agent.js'
+export * from './is-editable-element.js'