Always use a temp dir for cliplugin extractions
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Description

If we always extract to a temp dir (in the same partition where the intended destination folder is), we could simplify a lot the handling of cliplugins. Most importantly, we would not need anymore to check for those ugly`FileExistsExpression` and friends, since we would then move the extracted files ourselves to the final destination.

There is at least one blocker, though. If an archive has more than one file with the same name, in different subfolders, then when extracting the whole archive without preserving paths, the cliplugin is always going to be issue a "file already exists" prompt...

If we ever manage to use the cliplugins in a non-interactive way, we could probably also get rid of the KPtyProcess. See commit 053a28f0692 for the reason why it is (was?) necessary.