Added MacPorts solution for depext for a few conf packages

[MSoegtropIMC]

This PR adds a MacPorts solution for 4 conf packages which only had a homebrew solution on macOS.

What I am unsure about are the rules if an existing package should be modified or a package with a new / incremented version should be created. I followed what seems to be common practice for each individual package but ended up to do it differently. I would appreciate some general advice on this and some special advice for the case of adding a depext MacPorts solution.

Note: the handling of variants in MacPorts (like "gtk3 +quartz") doesn't look solid. It seems to work but depext treats this partly as separate packages (e.g. when listing what to install) and partly as one package (e.g. when sorting packages).

[camelus]

Commit: 40a94e7

Hello @MSoegtropIMC! I believe this is your first contribution here. Please be nice, reviewers!

🌩️ opam-lint errors 40a94e7

• conf-gnome-icon-theme3.0 has errors:

  • error 23: Missing field 'maintainer'

• conf-pkg-config.1.3 has errors:

  • error 46: Package is flagged "conf" but has source, install or remove instructions

• conf-gtk3.18 has some warnings:

  • warning 54: External dependencies should not contain spaces nor empty string: "gtk3 +quartz"

• conf-gtksourceview3.0+2 has some warnings:

  • warning 54: External dependencies should not contain spaces nor empty string: "gtksourceview3 +quartz"

---

☀️ Installability check (+2)

• new installable packages (2): conf-gtksourceview3.0+2 conf-pkg-config.1.3

[MSoegtropIMC]

Can someone tell me what to do about the errors?

• conf-gnome-icon-theme3.0 has errors:
  • error 23: Missing field 'maintainer'

This was so before

• conf-pkg-config.1.3 has errors:
  • error 46: Package is flagged "conf" but has source, install or remove instructions

The existing conf-pkg-config files should have the same issue

• conf-gtk3.18 has some warnings:
  • warning 54: External dependencies should not contain spaces nor empty string: "gtk3 +quartz"

For macports there is no way around this

• conf-gtksourceview3.0+2 has some warnings:
  • warning 54: External dependencies should not contain spaces nor empty string: "gtksourceview3 +quartz"

For macports there is no way around this

[mseri]

Thanks