refactor(editor): extract mobile extension builder (#12239)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Introduced a new mobile view extension that activates mobile-specific UI features based on the runtime environment.
  - Automatically enables mobile keyboard toolbar and linked document menu features in mobile contexts.

- **Improvements**
  - Simplified code and paragraph block configurations on mobile, including disabling line numbers and adjusting placeholders.
  - Enhanced configuration chaining to include mobile-specific settings by default.
  - Improved extension registration flow with method chaining support.

- **Refactor**
  - Removed deprecated mobile patch classes and configurations, consolidating mobile logic into dedicated extensions.
  - Streamlined mobile-related code for better maintainability and performance.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/ext-loader/src/base-provider.ts

@@ -17,7 +17,7 @@ export type Context<Scope extends string> = {
   /** The scope this context is associated with */
   scope: Scope;
   /** Function to register one or more extensions */
-  register(extensions: ExtensionType[] | ExtensionType): void;
+  register(extensions: ExtensionType[] | ExtensionType): Context<Scope>;
 };
 
 /**

blocksuite/affine/ext-loader/src/manager.ts

@@ -75,11 +75,14 @@ export class ExtensionManager<Scope extends string> {
 
   /** @internal */
   private readonly _getContextByScope = (scope: Scope): Context<Scope> => {
-    return {
+    const context: Context<Scope> = {
       scope,
-      register: (extensions: ExtensionType[] | ExtensionType) =>
-        this._registerToScope(scope, extensions),
+      register: (extensions: ExtensionType[] | ExtensionType) => {
+        this._registerToScope(scope, extensions);
+        return context;
+      },
     };
+    return context;
   };
 
   /**