RFC: Add option to enable sourcemap loader in develop mode

[fabiankaegy]

At 10up we are working with several self-maintained libraries, such as all of the component library packages and the block components package. Sometimes we run into issues with the actual library when working on projects.

Even though these libraries do ship sourcemaps they don't get loaded because only first-party code outputs its sourcemaps in the browser.

I would love to have an option built into toolkit that makes it possible to automatically load the sourcemaps from dependencies also in the dev bundle.

So loading the source-map-loader plugin in dev mode when a certain flag is enabled.

Maybe we can even restrict it to only @10up/ dependencies

[RuhaniMakhija]

Hello I would like to work on this issue