* multiplatform: relocated code to its new place
* code becomes better
* renamed file
* fixes for BASE64 and images, and changes for appFileUri
* different Base64 for both platforms
* fix file saving on long click
* platformCallbacks refactoring
* renamed callbacks to platform
* eol
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Co-authored-by: Evgeny Poberezkin <2769109+epoberezkin@users.noreply.github.com>