feat(build): add source when build

[hongrunhui]

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [x] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• [x] It's submitted to the main branch for v2.x (or to a previous version branch)
• [ ] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• [ ] All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• [ ] New/updated tests are included

If adding a new feature, the PR's description includes:

• [x] A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information: This way, we can generate Vue's sourcemap file, which helps us better understand Vue's source code. Sourcemap is a mapping file that maps compiled code back to the original source code, enabling us to debug and analyze in the browser.

Generating Vue's sourcemap file can help us:

Debug more efficiently by allowing us to easily view source code, set breakpoints, and analyze errors.

Learn Vue's source code more effectively by allowing us to track code execution flow, understand implementation mechanisms, and principles.