Re-remove webpack

[mjbvz]

All of our extensions are now using esbuild

[Copilot]

Pull request overview

This PR completes the removal of webpack from the built-in extensions build/packaging pipeline (now esbuild-only), while ensuring the Monaco test packaging step still has its own local webpack toolchain.

Changes:

• Remove webpack-based extension packaging/build support from build/lib/extensions.ts and build/gulpfile.extensions.ts.
• Drop shared webpack configuration and the (currently disabled) mangling loader from extensions/.
• Move webpack (and required loaders) into test/monaco so the Monaco “Package Editor with Webpack” workflow remains functional after root-level webpack deps are removed.

Reviewed changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/monaco/package.json	Uses local webpack binary and adds required webpack-related devDependencies for Monaco packaging.
test/monaco/package-lock.json	Locks the new Monaco-local webpack toolchain dependency graph.
package.json	Removes webpack-related devDependencies now that extensions no longer use webpack.
package-lock.json	Removes webpack-related packages from the root lockfile to match package.json.
extensions/shared.webpack.config.mjs	Deleted shared webpack config previously used by extensions.
extensions/mangle-loader.js	Deleted webpack loader previously used for (disabled) mangling.
build/lib/extensions.ts	Removes webpack packaging path; esbuild-only bundling remains.
build/gulpfile.extensions.ts	Stops discovering/running webpack configs for web extensions; esbuild-only.

Files not reviewed (1)

• test/monaco/package-lock.json: Language not supported