Add support for images and other MIME types with ThumbKey's internal clipboard

[jiquiame]

Describe your suggested feature

( From discussion #1762 (comment) )

Thumbkey internal clipboard / clipboard history currently only manages text and system clipboard needs to be used for clip data of other MIME types like pictures.

This makes the usage of clipboard history less practical, as well as complexifies the logic for the private clipboard paste. We should add it

Once this is added, the logic from #1762 can be changed as we can remove the boolean `wasLastCopyOperationDoneViaSystem

Other details

No response

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[Toldry]

Note for future implementer:
FlorisBoard is another open source android keyboard that has clipboard history with support for multiple MIME types. I suggest taking a look at their code to draw inspiration on how to implement it in ThumbKey.