Update ESLint, Prettier, tsconfig, and dependencies to modern versions

[Copilot]

Updates the project's tooling configuration to use modern versions and configurations, based on the changes from microsoft/vscode-cosmosdb#2673.

Key Changes

Configuration Updates

• ESLint: Migrated from legacy .eslintrc.js to modern eslint.config.mjs flat config format
• Prettier: Replaced .prettierrc with prettier.config.mjs using ES module syntax
• TypeScript: Updated tsconfig.json to use ES2023 target (Node.js 20.9+ fully supports it)

Dependency Updates

• Updated ESLint to v9.26.0 with typescript-eslint v8.32.0
• Updated language server packages to v9.0.1 (vscode-languageclient/vscode-languageserver)
• Added es-toolkit as a modern replacement for some lodash utilities
• Updated various dev dependencies to latest compatible versions

Code Modernization

• Replaced fs-extra with native Node.js node:fs/promises APIs
• Updated language server implementation to use modern v9 APIs
• Added helper utility pathExists for async file system checks
• Fixed test utilities to work with updated dependency interfaces

Build & Tooling

• Updated .vscodeignore to exclude new config files from packaging
• Added license headers to new configuration files
• Fixed TypeScript compilation errors related to updated APIs
• Ensured Prettier formatting works correctly with new config

Testing

• ✅ Build passes successfully
• ✅ Prettier formatting works correctly
• ✅ ESLint configuration loads and runs (shows some pre-existing code issues to address separately)
• ✅ Language server integration updated for v9 APIs

This modernization brings the project in line with current best practices while maintaining full functionality.

Fixes #168.

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[Copilot]

Pull Request Overview

This PR modernizes the project's development tooling configuration by migrating from legacy to modern standards and updating dependencies to their latest compatible versions.

• Updated ESLint from legacy .eslintrc.js to modern eslint.config.mjs flat config format
• Replaced .prettierrc with prettier.config.mjs using ES module syntax
• Updated TypeScript configuration to target ES2023 and modernized dependency APIs

Reviewed Changes

Copilot reviewed 60 out of 62 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
eslint.config.mjs	New modern ESLint flat config format with comprehensive rule sets
prettier.config.mjs	New Prettier config using ES module syntax
package.json	Updated all dev dependencies to latest versions with new eslint/prettier packages
webpack.config.*.js	Updated build targets to ES2023 and added dev server middleware fix
test/*	Replaced deprecated test utilities with local implementations
src/*	Updated imports from lodash to es-toolkit and fs-extra to native Node.js APIs

Comments suppressed due to low confidence (1)

src/webviews/documentdb/collectionView/components/QueryEditor.tsx:20

• [nitpick] The interface 'QueryEditorProps' should follow the project's naming convention. Consider using a more descriptive name like 'IQueryEditorProps' to align with other interface naming patterns in the codebase.

export const QueryEditor = ({ onExecuteRequest }: QueryEditorProps): JSX.Element => {