[Web] Support structural tag in web-xgrammar package, upgrade version to 0.1.27

[akaashrp]

1. Support structural tag in web-xgrammar package
2. Upgrade version to 0.1.27
3. Upgrade devDependencies and migrate to new eslint config format
4. Fix testing

[Copilot]

Pull request overview

This PR adds structural tag support to the web-xgrammar package and upgrades to version 0.1.27. It includes significant infrastructure updates including migration to ESLint 9 flat config format, Jest ESM support, and TypeScript configuration improvements.

Key Changes:

• Added comprehensive structural tag API with both modern and legacy interfaces
• Upgraded development dependencies (ESLint 9.x, Jest 30.x, TypeScript 5.9.x, Rollup 4.x)
• Migrated to ESLint flat config format and improved Jest ESM configuration
• Updated C++ bindings to support structural tag validation and compilation

Reviewed changes

Copilot reviewed 18 out of 19 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
web/package.json	Version bump to 0.1.27 and major devDependency upgrades
web/tsconfig.json	Added ES2022 target and module configuration for better ESM support
web/src/structural_tag.ts	New module providing structural tag type definitions and conversion utilities
web/src/xgrammar.ts	Extended Grammar and GrammarCompiler APIs with structural tag support
web/src/xgrammar_binding.cc	Added C++ wrapper functions for structural tag validation and compilation
web/src/index.ts	Exported new structural tag types and StructuralTagItem class
web/tests/grammar.test.ts	Updated tests for new API signatures and added structural tag test coverage
web/tests/web_tokenizers_shim.mjs	New shim module for CommonJS tokenizer compatibility in Jest ESM
web/jest.config.cjs	Enhanced ESM support with proper module name mapping
web/eslint.config.cjs	New flat config format replacing legacy .eslintrc.cjs
web/.eslintrc.cjs	Removed legacy ESLint configuration file
web/.eslintignore	Removed in favor of ignores in flat config
web/run_test.sh	Rewritten to use proper ESM test execution without package.json patching
web/build.sh	Updated CMake flag from BUILD_PYTHON_BINDINGS to XGRAMMAR_BUILD_PYTHON_BINDINGS
web/example/src/example.ts	Added structural tag example demonstrating new API usage
web/example/package.json	Version sync to 0.1.27 with dependency updates
cmake/config.cmake	Made XGRAMMAR_BUILD_PYTHON_BINDINGS conditionally defined
CMakeLists.txt	Added deprecation handling for old BUILD_PYTHON_BINDINGS flag

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