Use C++20 and CMake presets (#7322)

* Create tasks.json

* Delete gui.pro

* Swallow any exceptions from stopDesktop

* Upgrade to C++20

* Update ChangeLog

* Remove old versions of Ubuntu

* Ignore VS Code workspace

* Restore original CodeQL job name

* Add problem matcher and suppress warnings from within old CMake lib

* Bump CMake min version to 3.5

* Remove useless cmake_minimum_required

* HACK: temp comment out failing code

* Bump Qt to 5.12.6

* Delete tasks.json

* Create CMakePresets.json

* Fixed Qt link error: The input line is too long.

* Fixed invalid call to map erase

* Fixed incorrect use of RegCreateKeyEx

* Add VS Code tasks.json for cmake build

* Store `desktop` in char buf before using it

* Generate compile_commands.json

* Restore indentation

* Revert "Restore indentation"

This reverts commit d9f495460f337c37e8a01d8853b317e949ea085a.

* Restore original indentation (for now)

* Create extensions.json

.gitignore

@@ -32,3 +32,5 @@ flatpak/build
 flatpak/export
 flatpak/synergy.desktop
 flatpak/*.flatpak
+*.code-workspace
+*.idx