build-system/MXE: build with more up to date MXE tools.

- use hidapi grantlee and mdbtools from MXE
- update MXE version to use QT 5.15, and pull in libzstd and  CMake 3.17.3
- fix linking of winmm on windows build with new mxe
- add some instructions on building the container
- add some new dependancies from QT 5.15 to the packaging
- add a patch to MXE to Build qtconnectivity with native-win32-bluetooth

[Dirk Hohndel: small refactor]

Signed-off-by: Paul Buxton <paulbuxton.mail@googlemail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

scripts/docker/mxe-build-container/qtconnectivity-1.patch

@@ -0,0 +1,12 @@
+diff --git a/src/bluetooth/configure.json b/src/bluetooth/configure.json
+index 3bd95903..0d41d88f 100644
+--- a/src/bluetooth/configure.json
++++ b/src/bluetooth/configure.json
+@@ -63,6 +63,7 @@
+             "purpose": "Uses the native Win32 Bluetooth backend.",
+             "section": "Qt Bluetooth",
+             "autoDetect": false,
++            "enable": true,
+             "output": [ "publicFeature", "feature" ]
+         },
+         "winrt_bt": {