Setup.iss: user-mode install via /CURRENTUSER (PR-B)

Extends the existing Inno Setup installer with a /CURRENTUSER flag
that routes to a complete user-mode install path. Default behavior
(admin, system-mode) is unchanged.

User-mode (/CURRENTUSER) flow:
  1. Drift-detect: checks ProjFS enabled + EnableProjFSOnAllDrives
     task registered with current hash marker
  2. If drift detected: self-elevates via /ADMINSTAGE=true to enable
     ProjFS and register the task from pre-built embedded XML
  3. Deploys payload to %LocalAppData%\GVFS\Versions\<version>\
  4. Creates/swaps Current junction with verification + rollback
  5. Updates user PATH (HKCU) and GVFS env vars
  6. Registers per-user \GVFS\AutoMount logon task (conhost --headless)
  7. GCs old versions (keeps most recent 2)

Build changes:
  - GVFS.Installers.csproj: BuildProjFSTaskXml target runs
    build-task-xml.ps1 and passes output to ISCC
  - Setup.iss: PrivilegesRequiredOverridesAllowed=commandline

Review fixes incorporated:
  - /ADMINSTAGE=true (not bare /ADMINSTAGE) for Inno Setup param parsing
  - Junction rollback reads old target via fsutil reparsepoint query
    and actually restores it via mklink /J
  - Logon task XML declares UTF-8 encoding (matches SaveStringToFile)

Assisted-by: Claude Opus 4.8
Signed-off-by: Tyrie Vella <tyrielv@gmail.com>

Author: tyrielv

GVFS/GVFS.Installers/GVFS.Installers.csproj

@@ -3,6 +3,8 @@
   <PropertyGroup>
     <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
     <LayoutPath>$(RepoOutPath)GVFS.Payload\bin\$(Configuration)\win-x64\</LayoutPath>
+    <ProjFSAttachScriptsDir>$(MSBuildThisFileDirectory)..\..\scripts\projfs-attach\</ProjFSAttachScriptsDir>
+    <ProjFSTaskXmlPath>$(IntermediateOutputPath)enable-projfs-on-all-drives-task.xml</ProjFSTaskXmlPath>
   </PropertyGroup>
 
   <ItemDefinitionGroup>
@@ -24,8 +26,12 @@
     <Content Include="info.bat" />
   </ItemGroup>
 
+  <Target Name="BuildProjFSTaskXml" BeforeTargets="CreateInstaller" Condition="'$(SkipCreateInstaller)' != 'true'">
+    <Exec Command='powershell.exe -NoProfile -ExecutionPolicy Bypass -File "$(ProjFSAttachScriptsDir)build-task-xml.ps1" -ScriptPath "$(ProjFSAttachScriptsDir)enable-projfs-on-all-drives.ps1" -TemplatePath "$(ProjFSAttachScriptsDir)enable-projfs-on-all-drives-task.xml.template" -OutputPath "$(ProjFSTaskXmlPath)"' />
+  </Target>
+
   <Target Name="CreateInstaller" BeforeTargets="Build" Condition="'$(SkipCreateInstaller)' != 'true'">
-    <Exec Command='"$(PkgTools_InnoSetup)\tools\ISCC.exe" /DLayoutDir="$(LayoutPath)" /DGVFSVersion=$(GVFSVersion) Setup.iss /O"$(OutputPath)"' />
+    <Exec Command='"$(PkgTools_InnoSetup)\tools\ISCC.exe" /DLayoutDir="$(LayoutPath)" /DGVFSVersion=$(GVFSVersion) /DProjFSTaskXml="$(ProjFSTaskXmlPath)" Setup.iss /O"$(OutputPath)"' />
   </Target>
 
   <Target Name="CleanInstaller" BeforeTargets="AfterClean">