* Remove individual feature flags in favor of a single `KPXC_MINIMAL` flag that removes advanced features from the build. Basic features are no longer guarded by feature flags.
* Basic features: Auto-Type, Yubikey, KeeShare
* Advanced features include: Browser (and passkeys), SSH Agent, and Secret Service
* Networking, Documentation, and Update Checking remain as feature flags to accommodate various distro requirements.
This change also cleans up the main CMakeLists.txt by re-arranging some content and placing macros into a dedicated include file. The minimum CMake version was bumped to 3.16.0 to conform to our minimum Ubuntu support of Focal (20.04). This also allows us to default to C++20, we fall back to C++17 for Qt versions less than 5.15.0 due to lack of support.
Lastly this change removes the KEEPASSXC_BUILD_TYPE="PreRelease" which is never used. We only support "Snapshot" and "Release" now.
