GODT-1569: upgrade bridge from qt 5 to qt 6.

Fixed issues introduced by upgrading to Qt 5.15.
WIP: upgrade to Qt 6
WIP: QML fixes. [sklp-ci]
WIP: macOS font fix.
WIP: backend is a now a singleton.
WIP: remove version number of import.
WIP: fixed missing Action in qmldir.
WIP: fixed errors on program exit.
WIP: CMake detects host arch on mac if not specified.

internal/frontend/bridge-gui/README.md

@@ -1,5 +1,6 @@
 ## Prerequisite
 
+### Linux (debian and derivates)
 ```` bash
 sudo apt install build-essential
 sudo apt install tar curl zip unzip
@@ -7,22 +8,63 @@ sudo apt install linux-headers-$(uname -r)
 sudo apt install mesa-common-dev libglu1-mesa-dev
 ````
 
-## Define Qt5DIR
+### macOS & WIndows
 
-```` bash
-export QT5DIR=/opt/Qt/5.13.0/gcc_64
-````
+Coming soon...
 
-## install vcpkg and define VCPKG_ROOT
 
-```` bash
+###  Define QT6DIR
+
+``` bash
+export QT6DIR=/opt/Qt/6.3.1/gcc_64
+```
+
+### install vcpkg and define VCPKG_ROOT
+
+``` bash
 git clone https://github.com/Microsoft/vcpkg.git
 ./vcpkg/bootstrap-vcpkg.sh 
 export VCPKG_ROOT=$PWD/vcpkg
-````
+```
 
 ## install grpc & protobuf
 
-```` bash
+``` bash
 ./vcpkg install grpc
-````
+```
+
+## Building
+
+A simple script is provided that run the appropriate CMake command.
+
+``` bash
+./build.sh
+``` 
+
+## Running
+
+Simply run from the cmake build folder (`cmake-build-debug` by default) 
+``` bash
+./bridge-gui
+```
+
+`bridge-gui` will launch the `bridge` executable that it will try to locate in
+
+- The working directory.
+- The application directory.
+- `cmd/Desktop-Bridge/`, `../cmd/Desktop-Bridge/`,  `../../cmd/Desktop-Bridge` 
+(up to five parent folders above the current folder are inspected).
+
+you can specify the location of the bridge executable using the `-b` or 
+`--bridge-exe-path` command-line parameter:
+
+``` bash
+./bridge-gui -b "~/bin/bridge"
+```
+
+you can also ask bridge-gui to connect to an already running instance of `bridge`
+using the `-a` or `--attach` command line parameter.
+
+``` bash
+./bridge-gui -a
+```