refactor: reorganize specs and adapter extensions (#10359)

### TL;DR
Refactored `SpecProvider` singleton access pattern and reorganized adapter/extension code structure.

### What changed?
- Changed `SpecProvider.getInstance()` to `SpecProvider._` for cleaner singleton access
- Moved adapter/extension code from `_common` directory to dedicated `adapters` and `extensions` folders
- Consolidated adapter extensions into a single file
- Removed unused dependencies from package.json
- Deleted unnecessary schema files
- Extracted `MobileSpecsPatches` class into the mobile patching code
- Updated all references to use the new `SpecProvider._` accessor

### How to test?
- Verify all specs are properly registered and accessible via `SpecProvider._`
- Test adapter functionality for HTML, Markdown, Notion HTML and plain text
- Check mobile-specific features and patches work correctly
- Ensure preview functionality works in both page and edgeless modes

### Why make this change?
- Improves code organization by properly separating adapters and extensions
- Simplifies singleton access pattern
- Removes unnecessary dependencies and files
- Makes the codebase more maintainable by consolidating related functionality

blocksuite/playground/apps/_common/helper.ts

@@ -5,8 +5,7 @@ import { TestWorkspace } from '@blocksuite/store/test';
 export function createEmptyDoc() {
   const schema = new Schema().register(AffineSchemas);
   const collection = new TestWorkspace({ schema });
-  collection.storeExtensions =
-    SpecProvider.getInstance().getSpec('store').value;
+  collection.storeExtensions = SpecProvider._.getSpec('store').value;
   collection.meta.initialize();
   const doc = collection.createDoc();
 

blocksuite/playground/apps/starter/utils/collection.ts

@@ -56,8 +56,7 @@ export function createStarterDocCollection() {
     blobSources,
   };
   const collection = new TestWorkspace(options);
-  collection.storeExtensions =
-    SpecProvider.getInstance().getSpec('store').value;
+  collection.storeExtensions = SpecProvider._.getSpec('store').value;
   collection.start();
 
   // debug info