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

yarn.lock

@@ -4052,31 +4052,8 @@ __metadata:
     "@blocksuite/icons": "npm:^2.2.1"
     "@blocksuite/inline": "workspace:*"
     "@blocksuite/store": "workspace:*"
-    "@floating-ui/dom": "npm:^1.6.10"
-    "@lit/context": "npm:^1.1.2"
-    "@preact/signals-core": "npm:^1.8.0"
-    "@toeverything/theme": "npm:^1.1.11"
-    "@types/katex": "npm:^0.16.7"
-    "@types/lodash-es": "npm:^4.17.12"
-    "@vanilla-extract/css": "npm:^1.17.0"
     "@vanilla-extract/vite-plugin": "npm:^5.0.0"
-    date-fns: "npm:^4.0.0"
-    dompurify: "npm:^3.2.4"
-    fflate: "npm:^0.8.2"
-    file-type: "npm:^20.0.0"
-    fractional-indexing: "npm:^3.2.0"
-    html2canvas: "npm:^1.4.1"
-    katex: "npm:^0.16.11"
-    lit: "npm:^3.2.0"
-    lodash-es: "npm:^4.17.21"
-    lz-string: "npm:^1.5.0"
-    minimatch: "npm:^10.0.1"
-    nanoid: "npm:^5.0.7"
-    shiki: "npm:^2.0.0"
-    simple-xml-to-json: "npm:^1.2.2"
     vitest: "npm:3.0.6"
-    yjs: "npm:^13.6.21"
-    zod: "npm:^3.23.8"
   languageName: unknown
   linkType: soft