Update documentation to use correct Linux dependencies

[ann0see]

I have studied and tested this on both Raspbian 10 and 11, with the aim of making the script compatible with both. This is what I have found:

1. On 10, the package qt5-default does two main things: pull in qtbase5-dev as a dependency, and set the default version of Qt for qtchooser. Without this, there is no default version.
2. On 11, the package qt5-default does not exist. qtbase5-dev is still available as the main package to install, and the default version of Qt for qtchooser is automatically set to 5 by one of the installed dependencies.
3. Using qtchooser -list-versions is an OS-independent way of determining whether there is already a default or qt5-default is required.
4. Package qtdeclaractive5-dev is not required at all, as it only provides modules not used by Jamulus.
5. Package qttools5-dev-tools is available on both 10 and 11, and is required on 11 to provide lrelease for qmake.

So I would recommend the following section of code for installing packages on both 10 and 11 (I have tested on fresh installs of both):

# install required packages
pkgs='alsamixergui build-essential qtbase5-dev qttools5-dev-tools libasound2-dev cmake libglib2.0-dev'
if ! dpkg -s $pkgs >/dev/null 2>&1; then
  read -p "Do you want to install missing packages? " -n 1 -r
  echo
  if [[ $REPLY =~ ^[Yy]$ ]]; then
    sudo apt-get install $pkgs -y
    # Raspbian 10 needs qt5-default; Raspbian 11 doesn't need or provide it
    if ! qtchooser -list-versions | grep -q default; then
      sudo apt-get install qt5-default -y
    fi
  fi
fi

I have a version with this change at https://github.com/softins/jamulus/tree/fix-pi

Originally posted by @softins in #2267 (comment)

[hoffie]

Do you have any pointers wrt CI? I ran a quick grep and only found COMPILING.md, but nothing autobuild related.

[ann0see]

That was just an assumption. It should be here: https://github.com/jamulussoftware/jamulus/blob/master/autobuild/linux/autobuild_deb_1_prepare.sh

[ann0see]

It seems to be ok and very basic in the CI.

[softins]

That was just an assumption. It should be here: https://github.com/jamulussoftware/jamulus/blob/master/autobuild/linux/autobuild_deb_1_prepare.sh

That looks to specify exactly the same qt packages as I listed in the raspi script update. Cool, glad I came to the same conclusion. Assuming from that that Ubuntu 18 doesn't need qt5-default then, or the builds wouldn't work.

[softins]

Do you have any pointers wrt CI? I ran a quick grep and only found COMPILING.md, but nothing autobuild related.

Just looked at COMPILING.md. The Qt dependencies for Linux definitely need revising. I can make a PR for that, but need to check the differences between OS versions (Ubuntu, Debian and Raspbian) in order to be accurate.

[ann0see]

I just removed the CI part. It seems as if only the documentation needs to be updated

[hoffie]

We should also look into using --no-install-recommends. One of the dependencies (I think it's qttools5-dev-tools?) pulls in a whole lot of packages, including a full Xorg stack, which is totally overkill, especially on headless systems. Using that option might result in having to specify one or two other dependencies explicitly (qt5-qmake comes to mind).
(I haven't done any Raspberry-specific tests, but this is what I've found on Ubuntu. For autobuild, I'll keep track of the --no-install-recommends changes).