Cleanup dependency handling

Reason for the change

• Cleanup dependencies
• Reduce the number of unnecessary packages that are needed at build time

Changes

• Remove checks for Qt6QuickWidgets and Qt6QuickControls2. These are redundant as Qt6QuickWidgets is already searched for with the Quick component check in the Qt6 check. Similarly the Qt6QuickControls2 check is already satisfied by the QuickControls2 component check.
• kirigami and kirigami-addons are QML module dependencies that are only required at runtime, not buildtime. Adjust the checks to search for the QML modules instead.
• KF6QQC2DesktopStyle is a runtime dependency, not a build one.
• Adjust the packagers readme to reflect dependencies that are actually needed. Previously this was a copy of the output of feature_summary but that has several flaws. COMPONENTS checks are reported as "optional" even if they are required components, and required dependencies of packages are reported even though they really shouldn't (like Vulkan/OpenGL/XKB which are dependencies of Qt6 and may or may not even be required depending on how Qt6 is built).

Test plan

• Built elisa (no functional changes)