Add manifest tooling support for app.config.ts

[Krisztiaan]

Summary

• add manifest provider support for object-literal app.config.js and app.config.ts files
• keep JSON manifest behavior intact while extending links, diagnostics, and completions to dynamic config files
• add dynamic-config fixtures and focused VS Code e2e coverage for asset and local plugin workflows

Details

• expand manifest selectors to include app.config.js and app.config.ts
• add a lightweight TypeScript AST helper to find Expo config object literals, asset references, and plugin definitions
• teach manifest links, diagnostics, asset completions, and plugin completions to use those helpers for dynamic configs
• update the extension setting descriptions to reflect support for object-literal JS/TS configs

Verification

• npm run build
• npm run lint
• VSCODE_EXPO_TEST_PATTERN=dynamicManifest npm run test:vscode