Port to TypeScript: Infrastructure setup with gradual migration approach

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This PR establishes the foundation for migrating BlockPy to TypeScript while maintaining full backward compatibility with existing JavaScript code. The implementation uses a gradual migration strategy that allows both .js and .ts files to coexist seamlessly.

Key Changes

TypeScript Infrastructure

• Added TypeScript compiler configuration (tsconfig.json) with ES2017 target and modern module support
• Updated webpack configuration to handle .ts and .tsx files using ts-loader
• Extended ESLint configuration with TypeScript support via @typescript-eslint parser and plugins
• Added TypeScript build dependencies: typescript, ts-loader, and TypeScript ESLint tooling

Example Conversions

Two utility modules have been converted to demonstrate TypeScript benefits:

src/utilities.ts - Core utility functions with comprehensive type annotations:

export function arrayMove<T>(arr: T[], oldIndex: number, newIndex: number): T[]
export function capitalize(s: string | null | undefined): string
export function extractPart(text: string, partId: string | null | undefined): string | null

src/storage.ts - LocalStorage wrapper converted to a proper TypeScript class:

export class LocalStorageWrapper {
    constructor(namespace: string)
    set(key: string, value: string): void
    get(key: string): string | null
    has(key: string): boolean
}

Build System Integration

• Webpack now processes TypeScript files before Babel transformation
• Build commands (npm run build, npm run dev) work seamlessly with mixed JS/TS codebase
• TypeScript compilation can be tested independently with npx tsc --noEmit
• Zero breaking changes - all existing JavaScript functionality preserved

Documentation

• Created comprehensive migration guide (TYPESCRIPT_MIGRATION.md) with examples and best practices
• Updated README.md to highlight TypeScript support
• Documented development workflow and migration strategy

Benefits

1. Type Safety: Catch errors at compile time with comprehensive type checking
2. Enhanced Developer Experience: Better IDE support with autocomplete and refactoring
3. Self-Documenting Code: Type annotations serve as inline documentation
4. Gradual Adoption: No need to convert everything at once - perfect for incremental migration
5. Modern Development: Access to latest TypeScript features while maintaining ES2017 compatibility

Testing

• ✅ All existing builds continue to work without modification
• ✅ TypeScript compilation passes without errors
• ✅ Webpack processes both JS and TS files correctly
• ✅ ESLint handles mixed codebase appropriately
• ✅ Example TypeScript modules demonstrate full functionality

This foundation enables the development team to gradually migrate the remaining 46 JavaScript files to TypeScript at their own pace, with immediate benefits from enhanced tooling and type safety.

Fixes #132.

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