new directive `include_one`

[yashsinghcodes]

It would include all the files in the first directory and then from the second directory it would only import the files that weren't import before. So if the first directory contains a file called for example, "70_bar" then such file would be skipped when processing the second directory.

So currently I have only tested it my building the sway using following steps:

meson build/
ninja -C build/

I will mark it as draft for further testing on the command.

[emersion]

Note, we're not accepting new config-related features in general: https://github.com/swaywm/sway/blob/master/CONTRIBUTING.md#scope-of-future-changes-to-sway