feat(emacs)!: update script to latest spec

[wizard-28]

Updates the pacscript to the latest PKGBUILD spec https://aur.archlinux.org/cgit/aur.git/commit/?h=emacs-git&id=b9eb3b405717f8df37b38217dbb7d361b8ffca08

Closes #1303

[wizard-28]

@JonBoyleCoding Please test whether this works.

[wizard-28]

Also @Henryws this is a breaking change for the pacscript as a lot of deprecated features have been removed from it

[wizard-28]

@Henryws The CI doesn't work, jitterbit fails.

[JonBoyleCoding]

Sorry I haven't had the time to test this out. I won't have time until end of next week to do anything on the side - if you still need some help with this by then I can have a look then.

[Elsie19]

@wizard-28 can you look at the reviews?

[wizard-28]

For Ubuntu:

emacs : Depends: libgtk-3-dev but it is not going to be installed
         Depends: libwebp6 but it is not installable

For Debian:

 emacs : Depends: libjpeg-turbo8 but it is not installable
         Depends: libwebp6 but it is not installable

[wizard-28]

libwebp7 seems to be present in ubuntu:latest, but not libwebp6

libgtk-3-dev is present in ubuntu:latest, but not in ubuntu:devel and ubuntu:rolling

[wizard-28]

@Henryws what to do?

[Elsie19]

Maybe use incompatible

[wizard-28]

Maybe use incompatible

Should I add OS-specific dependencies?

[Elsie19]

Sure

[wizard-28]

@Henryws works, approve.