Scan image dialog is non-modal in x64 apps

[papeh]

Testable in FieldWorks (LT-21465).

• Compile SIL.Windows.Forms.TestApp for x64 (or include the ImageToolboxControl in some other x64 app)
• Open the Image Toolbox and click Scanner
• Click a window other than the Scanner dlg Expected: the Scanner dlg flashes and is focused Actual: the Scanner dlg disappears behind all other windows

This is not a problem in Any CPU or x86 apps using the x86 Interop.WIA.dll. It may be a problem with the MSIL Interop.WIA.dll

[papeh]

Perhaps a proper x64 DLL would fix this. Instructions to generate Interop.WIA.dll (from https://github.com/sillsdev/libpalaso/pull/1256):

• Add a COM reference to Microsoft Windows Image Acquisition
• Set Embed=false
• Copy generated assembly from the output into the lib folder
• Remove the COM reference