cMake: Add support for compiling against Qt6 (#7647)

Removes the BUILD_QT5 flag and adds a new FREECAD_QT_VERSION option,
which can be set to either "Auto" (default), 5, or 6. Auto detects which
version of Qt is installed on the system and chooses it. If both version
are installed, Qt5 is used.

Note that this DOES NOT implement compiling against Qt6, it only adds
the necessary cMake infrastructure to begin work on the source code
changes that will be required.

src/Mod/Web/App/CMakeLists.txt

@@ -7,20 +7,13 @@ include_directories(
     ${ZLIB_INCLUDE_DIR}
 )
 
-if(BUILD_QT5)
-    include_directories(
-        ${Qt5Network_INCLUDE_DIRS}
-    )
-    set(Web_LIBS
-         FreeCADApp
-         ${Qt5Network_LIBRARIES}
-    )
-else()
-    set(Web_LIBS
-         FreeCADApp
-         ${QT_LIBRARIES}
-    )
-endif()
+include_directories(
+    ${QtNetwork_INCLUDE_DIRS}
+)
+set(Web_LIBS
+    FreeCADApp
+    ${QtNetwork_LIBRARIES}
+)
 
 SET(Web_SRCS
     AppWeb.cpp

src/Mod/Web/CMakeLists.txt

@@ -7,7 +7,7 @@ set(Web_Scripts
 )
 
 if(BUILD_GUI)
-    if(Qt5WebEngineWidgets_FOUND OR Qt5WebKitWidgets_FOUND OR QT_QTWEBKIT_FOUND)
+    if(QtWebEngineWidgets_FOUND)
         add_subdirectory(Gui)
         list (APPEND Web_Scripts InitGui.py)
     endif()

src/Mod/Web/Gui/CMakeLists.txt

@@ -7,28 +7,17 @@ include_directories(
     ${XercesC_INCLUDE_DIRS}
 )
 
-if (Qt5WebEngineWidgets_FOUND)
+if (QtWebEngineWidgets_FOUND)
     add_definitions(-DQTWEBENGINE)
-elseif(Qt5WebKitWidgets_FOUND OR QT_QTWEBKIT_FOUND) # Qt5 and Qt4
-    add_definitions(-DQTWEBKIT)
 endif()
 
 set(WebGui_LIBS
     FreeCADGui
 )
 
-if(BUILD_QT5)
-    if(Qt5WebEngineWidgets_FOUND)
-        include_directories(${Qt5WebEngineWidgets_INCLUDE_DIRS})
-        list(APPEND WebGui_LIBS ${Qt5WebEngineWidgets_LIBRARIES})
-    else()
-        include_directories(${Qt5WebKitWidgets_INCLUDE_DIRS})
-        list(APPEND WebGui_LIBS ${Qt5WebKitWidgets_LIBRARIES})
-    endif()
-    qt5_add_resources(Web_QRC_SRCS Resources/Web.qrc)
-else()
-    qt4_add_resources(Web_QRC_SRCS Resources/Web.qrc)
-endif()
+include_directories(${QtWebEngineWidgets_INCLUDE_DIRS})
+list(APPEND WebGui_LIBS ${QtWebEngineWidgets_LIBRARIES})
+qt_add_resources(Web_QRC_SRCS Resources/Web.qrc)
 
 SET(WebGui_SRCS
     ${Web_QRC_SRCS}
@@ -40,8 +29,8 @@ SET(WebGui_SRCS
     Workbench.h
     BrowserView.h
     BrowserView.cpp
-    CookieJar.cpp   # QWebkit only
-    CookieJar.h     # QWebkit only
+    CookieJar.cpp
+    CookieJar.h
 )
 
 SET(WebGuiIcon_SVG