chore(devextreme): replace gulp js-bundles-prod with nx bundle executor

[chaosmirage]

No description provided.

[Copilot]

Pull request overview

This PR migrates DevExtreme’s production JS bundle step away from the Gulp js-bundles-prod task to the devextreme-nx-infra-plugin:bundle Nx executor, aligning bundling with the monorepo’s Nx-based build pipeline.

Changes:

• Adjusts the Nx bundle executor’s webpack config assembly (createWebpackConfig).
• Reworks packages/devextreme Nx targets to build prod bundles via bundle:prod:build and apply license headers via a unified bundle:headers target (with a prod configuration).
• Updates bundle:prod to run Nx commands instead of gulp js-bundles-prod.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
packages/nx-infra-plugin/src/executors/bundle/executor.ts	Changes webpack optimization handling for bundles produced by the Nx executor.
packages/devextreme/project.json	Replaces the Gulp prod bundling command with Nx bundle + license-header steps; refactors header target naming/configurations.