`.filters` files not being fully cleaned up by LvglProjectFileUpdater

[vwheeler63]

LvglProjectFileUpdater project has 3 places where .vcxproj.filters files are loaded, records removed before a new set of filter records are added. However, for all 3 projects that it maintains, it is not removing all the filter records first as intended. The result of this is that the records that are not removed remain in the file and accumulate when the new filter records are added. This is visible, for example, in LvglWindowsSimulator.vcxproj.filters where there are 28 occurrences of a record that looks like this with the only difference being the GUID:

    <Filter Include="lvgl">
      <UniqueIdentifier>{f5912e4b-3b50-4c96-b7f0-a894ec1379cf}</UniqueIdentifier>
    </Filter>

and 28 occurrences of a record that looks like this, again with the only difference being the GUID:

    <Filter Include="freetype">
      <UniqueIdentifier>{eb1a5e6c-513b-4ffc-803b-a85ca5aa4d0a}</UniqueIdentifier>
    </Filter>

I believe the reason for this is that with the trailing backslash on Program.cs line 188 and 190 respectively.

The other .filters files maintained by this project have similar problems, due to the same cause:

• LvglWindowsDesktopApplication.vcxproj.filters -- Program.cs line 327, and
• LvglWindowsStatic.vcxproj.filters -- LvglWindowsLibraryProjectUpdater.cs line 189.