Enable rebuilding FFMPEG for MSVC without deleting lib files first

To simplify testing modifications to the FFMPEG library, it is nice to
be able to rebuild FFMPEG without having to manually delete lib files
first. This change makes this possible because it uses powershell
Move-Item instead of Rename-Item to rename .o files to .lib files.
Move-Item's -Force argument allows renaming files to destination that
already exists.

Pick-to: 6.5 6.6
Change-Id: I0a56776d38c37d38d1cd74b5186881fc955d51f0
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>

coin/provisioning/common/windows/install-ffmpeg.ps1

@@ -83,7 +83,11 @@ function InstallMsvcFfmpeg {
         Write-Host "Rename libraries lib*.a -> *.lib"
         try {
             $msvcDir = [System.Environment]::GetEnvironmentVariable("FFMPEG_DIR_MSVC", [System.EnvironmentVariableTarget]::Machine)
-            Get-ChildItem "$msvcDir\lib\lib*.a" | Rename-Item -NewName { $_.Name -replace 'lib(\w+).a$', '$1.lib' }
+            Get-ChildItem "$msvcDir\lib\lib*.a" | ForEach-Object {
+                $NewName = $_.Name -replace 'lib(\w+).a$', '$1.lib'
+                $Destination = Join-Path -Path $_.Directory.FullName -ChildPath $NewName
+                Move-Item -Path $_.FullName -Destination $Destination -Force
+            }
         } catch {
             Write-Host "Failed to rename libraries lib*.a -> *.lib"
             return $false