Introduce gUiAppFileGuid: it has the same value of UiApp guid defined in
the .inf file. This is used to register UiApp as a boot entry in the
BootManagerMenu.
This registration is done in PlatformBootManagerBeforeConsole because
it must be done before the hotkeys are registered. This is because
in a system with hotkeys still bound to UiApp, but with firmware disabled,
you can still boot into the latter by hitting ESC or F2 during boot.
UiApp can be enabled/disabled using fw_cfg option FirmwareSetupSupport
Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
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