emulators/retroarch: Update to 1.7.4.

Changes:

    CHEEVOS: Fix crash when scrolling Achievement List while Unofficial Achievements enabled (#6732).
    CHEEVOS: Added hitcounts support for PauseIf/ResetIf (#6817).
    COMMON: Automatically hide "Configuration Override options" in Quick Menu.
    COMMON: Small Bugfix to not trigger savestate code when pressing Reset.
    COMMON: Added libsixel video driver.
    EMSCRIPTEN: Fix Game Focus Toggle.
    HID/OSX: Fix to set hid device registration deterministic (#6497), to address issue #6640 re-adding dynamic device registration.
    LOCALIZATION: Update Italian translation.
    LOCALIZATION: Update Japanese translation.
    LOCALIZATION: Update Polish translation.
    LOCALIZATION: Update Portuguese / Brazilian translation.
    LOCALIZATION: Update Russian translation.
    LOCALIZATION: Update Spanish translation.
    MIDI: Add MIDI support to the libretro API. Dosbox is the first proof of concept core implementing libretro MIDI.
    MIDI: Add a Windows driver for MIDI, based on winmm.
    MENU/QT/WIMP: Qt QSlider styling for Dark Theme.
    MENU/QT/WIMP: Remove button ghostly inside highlighting.
    MENU/QT/WIMP: Initial grid view.
    MENU/QT/WIMP: Drag&drop to add new playlist items, add option to add/edit/delete playlists.
    MENU/QT/WIMP: Add menu option to update RetroArch (Windows only for now).
    MENU/QT/WIMP: Add menu option to manage shaders.
    MENU/QT/WIMP: Add menu option to manage core options.
    MENU/XMB: Add new icons for the settings
    MENU/XMB: Add an option to show the desktop ui
    METAL: Initial work-in-progress video driver for Metal. macOS-only right now, and currently requires macOS 10.13.
    METAL: Supports XMB/MaterialUI, has a menu display driver. Has a font rendering driver.
    METAL/SLANG: Slang shaders should be compatible with Metal video driver.
    NETWORK: Enable SSL/TLS support by default for desktop platforms.
    QNX: Fix Game Focus Toggle.
    REMAPS: Fix the way offsets are calculated for keyboard remapping.
    RUNAHEAD: Fix full-screen mode change breaking Secondary Core's environment variables.
    VULKAN: Fix two validation errors.
    VULKAN: Try to avoid creating swapchains redundantly. Should fix black screen and having to alt tab out of window again to get display working on Nvidia GPUs (Windows).
    VULKAN/OSX: Initial MoltenVK support. Not enabled yet, several MoltenVK bugs should be fixed first before we can have it fully working.
    X11: Fix Game Focus Toggle.

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