[feat][clipboard-manager] Add "readImagePNG()" method

[WolfBearGames]

I am using the clipboard-manager plugin and readImage() in JS to get an image from the clipboard. The method returns the data as an uncompressed rgba bytes array which results in over 100MB for a screenshot of a UHD Desktop. This results in multiple seconds of wait time and is very inefficient.

A new readImagePNG() method could transfer the data as a PNG resulting a less data that need to be transferred.

The code for this already exists, before it was changed:
d57df4d

It should be relatively easy to add a readImagePNG() as an additional option in the clipboard-manager plugin.
(Alternatively, the readImage() method could accept a paramater which format to return)