handle images in win32 clipboard

[Antoine Martin]

From ticket:2603#comment:3, the data will look like this:

Error: failed to get clipboard data
 no matching format in DataObject, System.Drawing.Bitmap, CF_BITMAP, Ole Private Data, CF_DIB, CF_DIBV5

And maybe we can re-use the screen capture code to handle BITMAP and / or DIB.

Generic ticket for exotic clipboard formats: #273

[Antoine Martin]

As of r26546, we can copy from images from the windows clipboard.

TODO:

• use pillow ​imagegrab to simplify the code?
• handle transparency
• add watermark (generalize the existing code)
• other direction: copy to the clipboard

[Antoine Martin]

Updates:

• r26547 copy images to the clipboard
• r26549 + r26551: support compressed PNG and JPEG binary formats

TODO: watermark, sanitize binary image data through PIL?

[Antoine Martin]

• r26553 re-uses the same code as X11 for adding watermarks (disabled by default), adding a timestamp (now also disabled) and sanitizing the data (enabled by default)
• r26554 skips sanitizing when not needed (when we already generated the compressed image data via python-pillow ourselves)

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/2619