Treat focusable as enumerated boolean attribute

Author: gaearon

packages/react-dom/src/shared/DOMProperty.js

@@ -260,7 +260,12 @@ const properties = {};
 // In React, we let users pass `true` and `false` even though technically
 // these aren't boolean attributes (they are coerced to strings).
 // Since these are SVG attributes, their attribute names are case-sensitive.
-['autoReverse', 'externalResourcesRequired', 'preserveAlpha'].forEach(name => {
+[
+  'autoReverse',
+  'externalResourcesRequired',
+  'focusable',
+  'preserveAlpha',
+].forEach(name => {
   properties[name] = new PropertyInfoRecord(
     name,
     BOOLEANISH_STRING,