Enable deb package generation with cpack

[ooshlablu]

This adds the variables necessary for cpack to generate a deb package right from this project, and enables the generation of the dependencies section of the deb via dpkg-shlibdeps (installed via the dpkg-dev package in Debian, Ubuntu, and Mint).

To build a debian package using this pull request:

## Follow the usual steps from the docs, but create a branch using this PR
git clone https://github.com/dolphin-emu/dolphin.git dolphin-emu
cd ./dolphin-emu
git fetch origin pull/10170/head:pr10170
git checkout pr10170
git submodule update --init
mkdir Build && cd Build

## Specify the package contact (Required for building debs with cpack)
cmake -DCPACK_PACKAGE_CONTACT="Your Name Here" ..
make -j$(nproc)

## instead of 'make install' generate the deb
cpack -G DEB

[phire]

I'm not sure if we should be setting CPACK_PACKAGE_CONTACT. That should be done by the person actually building the package.

We don't want to end up as the contact for packages done by someone else.

[ooshlablu]

I'm not sure if we should be setting CPACK_PACKAGE_CONTACT. That should be done by the person actually building the package.

We don't want to end up as the contact for packages done by someone else.

Yeah, I'm open to suggestions. It is required to generate deb packages with cpack. I'll throw my name in there if necessary :-)

[phire]

Yes, but it shouldn't be baked in.

Modify your package building instructions to tell the maintainer to add their name during configuration:

cmake .. -DCPACK_PACKAGE_CONTACT="Your Name Here"

[Rumi-Larry]

Ammending your commit to fix mistakes or for minor changes, is always better than making a new one. Just fyi, because you will need to squash those commits anyway.

[Drex-C137]

So that it doesn't happen to anyone else again, here is a list of dependencies that I had to install so that the project would compile without errors. I did this on Linux Mint 21.3 (Ubuntu / Debian based)

sudo apt install build-essential libgl1-mesa-dev libx11-dev libudev-dev libegl1 libxi-dev libevdev-dev qtbase5-dev qtbase5-private-dev