[qt] refactor: qt_common lib (#94)

This is part of a series of PRs made in preparation for the QML rewrite. this PR specifically moves a bunch of utility functions from main.cpp into qt_common, with the biggest benefit being that QML can reuse the exact same code through ctx passthrough.

Also, QtCommon::Frontend is an abstraction layer over several previously Widgets-specific stuff like QMessageBox that gets used everywhere. The idea is that once QML is implemented, these functions can have a Quick version implemented for systems that don't work well with Widgets (sun) or for those on Plasma 6+ (reduces memory usage w/o Widgets linkage) although Quick from C++ is actually anal, but whatever.

Other than that this should also just kinda reduce the size of main.cpp which is a 6000-line behemoth rn, and clangd straight up gives up with it for me (likely caused by the massive amount of headers, which this DOES reduce).

In the future, I probably want to create a common strings lookup table that both Qt and QML can reference--though I'm not sure how much linguist likes that--which should give us a way to keep language consistent (use frozen-map).

TODO: Docs for Qt stuff

Co-authored-by: MaranBr <maranbr@outlook.com>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/94
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: Shinmegumi <shinmegumi@eden-emu.dev>

src/android/app/src/main/res/values-uk/strings.xml

@@ -495,8 +495,6 @@
     <string name="use_custom_rtc">Свій RTC</string>
     <string name="use_custom_rtc_description">Дозволяє встановити власний час (Real-time clock, або RTC), відмінний від системного.</string>
     <string name="set_custom_rtc">Встановити RTC</string>
-    <string name="disable_nca_verification">Вимкнути перевірку NCA</string>
-    <string name="disable_nca_verification_description">Вимкає перевірку цілісності архівів вмісту NCA. Може покращити швидкість завантаження, але ризикує пошкодженням даних або тим, що недійсні файли залишаться непоміченими. Необхідно для роботи ігор та оновлень, які вимагають прошивки 20+.</string>
 
     <!-- Network settings strings -->
     <string name="generate">Створити</string>