Use F8+F12 to release mouse on all platforms

It seems that Ctrl+End was used on non-Win32 platforms because
WxWidgets couldn’t use non-modifier keys as a keyboard sequence.  Qt
can, and F8+F12 interferes with the operation of software a lot less
than Ctrl+End does (try doing some text editing!).

86Box hasn’t used WxWidgets for quite some time and this platform
limitation hack has long outlived its necessity.

src/qt/qt_platform.cpp

@@ -583,6 +583,8 @@ c16stombs(char dst[], const uint16_t src[], int len)
 }
 #endif
 
+#    define MOUSE_CAPTURE_KEYSEQ "F8+F12"
+
 #ifdef _WIN32
 #    if defined(__amd64__) || defined(_M_X64) || defined(__aarch64__) || defined(_M_ARM64)
 #        define LIB_NAME_GS   "gsdll64.dll"
@@ -592,12 +594,10 @@ c16stombs(char dst[], const uint16_t src[], int len)
 #        define LIB_NAME_GPCL "gpcl6dll32.dll"
 #    endif
 #    define LIB_NAME_PCAP        "Npcap"
-#    define MOUSE_CAPTURE_KEYSEQ "F8+F12"
 #else
 #    define LIB_NAME_GS          "libgs"
 #    define LIB_NAME_GPCL        "libgpcl6"
 #    define LIB_NAME_PCAP        "libpcap"
-#    define MOUSE_CAPTURE_KEYSEQ "Ctrl+End"
 #endif
 
 QMap<int, std::wstring> ProgSettings::translatedstrings;