Fix: cache DocsContext on window to prevent duplication

This is intended to solve storybookjs/builder-vite#40
and related issues.

addons/docs/src/blocks/DocsContext.ts

@@ -1,4 +1,5 @@
 import { Context, createContext } from 'react';
+import { window as globalWindow } from 'global';
 
 export interface DocsContextProps {
   id?: string;
@@ -17,4 +18,15 @@ export interface DocsContextProps {
   forceRender?: () => void;
 }
 
-export const DocsContext: Context<DocsContextProps> = createContext({});
+// We add DocsContext to window. The reason is that in case DocsContext.ts is
+// imported multiple times (maybe once directly, and another time from a minified bundle)
+// we will have multiple DocsContext definitions - leading to lost context in
+// the React component tree.
+// This was specifically a problem with the Vite builder.
+/* eslint-disable no-underscore-dangle */
+if (globalWindow.__DOCS_CONTEXT__ === undefined) {
+  globalWindow.__DOCS_CONTEXT__ = createContext({});
+  globalWindow.__DOCS_CONTEXT__.displayName = 'DocsContext';
+}
+
+export const DocsContext: Context<DocsContextProps> = globalWindow.__DOCS_CONTEXT__;