How to create your own folder with classes in the Vendor folder (from the libraries installed by Composer)?

Question

PHP

When I was working with the google api, I had previously installed libraries for easy work with the google api using the composer. I liked that I could use Google classes without assigning a namespace to them.
How to create to make my libraries, after being loaded by the composer, placed in the vendor and work the same way?
More precisely, how to create such classes in this folder. The question is how to put it on the github so that others can also download and use the secondary one.