Update Development Prerequisites to qt6

[dfrap]

It is no longer possible to compile with qt5. The required packages should be updated to qt6.
On current stable Debian 12, I find these are enough to compile correctly:
qt6-svg-dev qt6-tools-dev qt6-base-dev qt6-multimedia-dev

It is not possible to install current releases on Debian, so compiling seems to be the best option.

[matty0ung]

I have updated the https://github.com/Brewtarget/brewtarget/wiki/Development:-Getting-Started page. I haven't tested the bt script etc on Debian, but I'd hope it mostly works given how much of Debian is used by Ubuntu. Give me a shout if you hit particular problems.

[dfrap]

The bt script had an error on Debian 12 that was easy to resolve: meson.build:191:0: ERROR: Value "c++23" (of type "string") for combo option "C++ language standard to use" is not one of the choices.
"g++ --version" returned g++ (Debian 12.2.0-14) 12.2.0
My 'fix' was to change to 'cpp_std=c++20' after line 191 of meson.build
Building and installing locally with Meson then worked well.
I do not suggest this part of the code be changed in the master since it only affects someone compiling on Debian. The local fix is easy to figure out and 'sticks' across compiles. Leave it at c++23 in the master for compiling on Ubuntu.

I was able to build a .deb install file with Meson, but it fails to install on Debian 12 because of dependency issues.
Even after accounting for the changes in #890 there are 4 more files that need changes in the control file.
brewtarget depends on lib32gcc-s1 (>= 12.3.0); however:
Version of lib32gcc-s1 on system is 12.2.0-14.
brewtarget depends on lib32stdc++6 (>= 12.3.0); however:
Version of lib32stdc++6 on system is 12.2.0-14.
brewtarget depends on libgcc-s1 (>= 12.3.0); however:
Version of libgcc-s1:amd64 on system is 12.2.0-14.
brewtarget depends on libstdc++6 (>= 12.3.0); however:
Version of libstdc++6:amd64 on system is 12.2.0-14.

[dfrap]

I just created a new .deb install file. There were only 3 dependencies that were an issue.
Unpacking brewtarget (4.0.12-1) ...
dpkg: dependency problems prevent configuration of brewtarget:
brewtarget depends on lib32stdc++6 (>= 12.3.0); however:
Version of lib32stdc++6 on system is 12.2.0-14.
brewtarget depends on libgcc-s1 (>= 12.3.0); however:
Version of libgcc-s1:amd64 on system is 12.2.0-14.
brewtarget depends on libstdc++6 (>= 12.3.0); however:
Version of libstdc++6:amd64 on system is 12.2.0-14.

[matty0ung]

Hopefully this is fixed in 4.0.12. If not, please don't hesitate to reopen this issue!