refactor(web): Extract VirtualScrollManager base class from TimelineManager (#23017)

Extract common virtual scrolling functionality from TimelineManager into
a new abstract VirtualScrollManager base class. This refactoring improves
code organization and enables reuse of virtual scrolling logic.

Changes:
- Create new VirtualScrollManager abstract base class with common virtual
  scrolling state and methods
- Refactor TimelineManager to extend VirtualScrollManager
- Rename 'assetsHeight' to 'bodySectionHeight' for semantic clarity
- Convert methods to use override keyword where appropriate
- Enable noImplicitOverride in tsconfig for better type safety
- Fix ApiError and AbortError class definitions with override keywords

web/tsconfig.json

@@ -6,6 +6,7 @@
     "forceConsistentCasingInFileNames": true,
     "module": "es2022",
     "moduleResolution": "bundler",
+    "noImplicitOverride": true,
     "resolveJsonModule": true,
     "skipLibCheck": true,
     "sourceMap": true,