Fix: Dangerzone installed using an msi built with WiX Toolset v3 is not uninstalled by an msi built with WiX Toolset v5

Fix the issue by adding some extra functionality to the "Next" button on the welcome screen of the installer. When the user clicks it to proceed with the installation this:
1. Flips the install scope to "perUser" which is the default in WiX v3
2. Finds the older installation
3. And finally flips the scope back to "perMachine" which is the default in WiX v4 and newer

TODO: Revert this once we are reasonably certain there are no affected Dangerzone Installations?

install/windows/build-app.bat

@@ -28,7 +28,6 @@ REM validate Dangerzone.msi
 wix msi validate Dangerzone.msi
 
 REM code sign Dangerzone.msi
-wix msi inscribe Dangerzone.msi
 signtool.exe sign /v /d "Dangerzone" /a /n "Freedom of the Press Foundation" /fd sha256 /t http://time.certum.pl/ Dangerzone.msi
 
 REM verify the signature of Dangerzone.msi

install/windows/build-wxs.py

@@ -84,9 +84,7 @@ def main():
     with open(version_filename) as f:
         # Read the Dangerzone version from share/version.txt, and remove any potential
         # -rc markers.
-        dangerzone_version = f.read().strip().split("-")[0]
+        version = f.read().strip().split("-")[0]
-
-    dangerzone_product_upgrade_code = "12B9695C-965B-4BE0-BC33-21274E809576"
 
     build_dir = os.path.join(
         os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))),
@@ -124,18 +122,17 @@ def main():
         "Package",
         Name="Dangerzone",
         Manufacturer="Freedom of the Press Foundation",
-        UpgradeCode=dangerzone_product_upgrade_code,
+        UpgradeCode="12B9695C-965B-4BE0-BC33-21274E809576",
         Language="1033",
         Compressed="yes",
         Codepage="1252",
-        Version=dangerzone_version,
+        Version=version,
     )
-
     ET.SubElement(
         package_el,
         "SummaryInformation",
         Keywords="Installer",
-        Description="Dangerzone " + dangerzone_version + " Installer",
+        Description="Dangerzone " + version + " Installer",
         Codepage="1252",
     )
     ET.SubElement(package_el, "MediaTemplate", EmbedCab="yes")
@@ -155,22 +152,40 @@ def main():
         Id="ARPURLINFOABOUT",
         Value="https://freedom.press",
     )
+    ET.SubElement(
+        package_el,
+        "WixVariable",
+        Id="WixUILicenseRtf",
+        Value="..\\install\\windows\\license.rtf",
+    )
+    ET.SubElement(
+        package_el,
+        "WixVariable",
+        Id="WixUIDialogBmp",
+        Value="..\\install\\windows\\dialog.bmp",
+    )
+    ET.SubElement(
+        package_el,
+        "MajorUpgrade",
+        AllowSameVersionUpgrades="yes",
+        DowngradeErrorMessage="A newer version of [ProductName] is already installed. If you are sure you want to downgrade, remove the existing installation via Programs and Features.",
+    )
 
+    # Add The UI element
     ui_el = ET.SubElement(package_el, "UI")
-
     ET.SubElement(
         ui_el, "ui:WixUI", Id="WixUI_InstallDir", InstallDirectory="INSTALLFOLDER"
     )
     ET.SubElement(ui_el, "UIRef", Id="WixUI_ErrorProgressText")
 
-    # Workaround for an issue after upgrading from WiX Toolset 3 to 5 where the older
+    # Workaround for an issue after upgrading from WiX Toolset v3 to v5 where the older
     # version of Dangerzone is not uninstalled during the upgrade
     #
-    # Work around the issue by adding some extra functionality to the "Next" button on the welcome screen
+    # Fix the issue by adding some extra functionality to the "Next" button on the welcome screen
     # of the installer. When the user clicks it to proceed with the installation this:
-    # 1. Flips the install scope to "perUser" which is the default in WiX 3
+    # 1. Flips the install scope to "perUser" which is the default in WiX v3
     # 2. Finds the older installation
-    # 3. And finally flips the scope back to "perMachine" which is the default in WiX 4 and newer
+    # 3. And finally flips the scope back to "perMachine" which is the default in WiX v4 and newer
     #
     # Adapted from this stack overflow answer: https://stackoverflow.com/a/35064434
     #
@@ -200,32 +215,13 @@ def main():
         Value="1",
     )
 
-    ET.SubElement(
-        package_el,
-        "WixVariable",
-        Id="WixUILicenseRtf",
-        Value="..\\install\\windows\\license.rtf",
-    )
-    ET.SubElement(
-        package_el,
-        "WixVariable",
-        Id="WixUIDialogBmp",
-        Value="..\\install\\windows\\dialog.bmp",
-    )
-    ET.SubElement(
-        package_el,
-        "MajorUpgrade",
-        AllowSameVersionUpgrades="yes",
-        DowngradeErrorMessage="A newer version of [ProductName] is already installed. If you are sure you want to downgrade, remove the existing installation via Programs and Features.",
-    )
-
     # Add the ProgramMenuFolder StandardDirectory
     programmenufolder_el = ET.SubElement(
         package_el,
         "StandardDirectory",
         Id="ProgramMenuFolder",
     )
-
+    # Add a shortcut for Dangerzone in the Start menu
     shortcut_el = ET.SubElement(
         programmenufolder_el,
         "Component",
@@ -259,14 +255,14 @@ def main():
         Id="ProgramFiles64Folder",
     )
 
-    # Generate the directory layout for the installed product
+    # Create the directory structure for the installed product
     build_directory_xml(programfilesfolder_el, data)
 
+    # Create a component group for application components
     applicationcomponents_el = ET.SubElement(
         package_el, "ComponentGroup", Id="ApplicationComponents"
     )
-
+    # Populate the application components group with components for the installed package
-    # Generate the components for the installed product
     build_components_xml(applicationcomponents_el, data)
 
     # Add the Feature element