[Feature Request] Remove ‘*.map‘ files from nupkg

**Is your feature request related to a problem? Please describe.**
Currently docfx NuGet package is relatively large size (about `72 MB`).
And almost size is occupied by template's source map(`.map`) files.
For example. `modern` template is about 36MB and `.map` files occupies 26.6MB. (about 73%)

If it can reduce `nupkg` size.
It can save local disk space and faster install/update.

**Describe the solution you'd like**
Disable `sourcemap` option when publishing packages.

**Downsides**
- Template relating bug report might be a bit harder to track down a problem.
- Can't view/debug javascript code from Developer Tools of browser by default.
(It needs manually adding source mapping (https://developer.chrome.com/docs/devtools/developer-resources/#load))

**Describe alternatives you've considered**
Another approach to reduce `nupkg` size is to merge `templates` folders that contains duplicated files. (#8691)

**Additional context**
Related issue/discussion
- #8785