Update build script to generate production scripts individually

[Tabrisrp]

Context
The current build command generates multiple production scripts at the same time.

Expected beavhior
We should have a command to build each script individually, and one command to build everything.

[wordpressfan]

I created this PR: #6625 to validate the idea with you before completing the code there.

As u can see, I created a new directory for gulp inside src/js with the following structure:

and as an example, I created a simple task module css which defines gulp tasks based on the data passed from the gulpconfig.js file.

We can do another task module for js, also I need to enhance the watch and build params so if we built the code many times to only get one version without any other changes until a change in the source file happens.

[Miraeld]

Looks ok to me