Revert "Restore clipboard history for editor by using ExClipboard instead of directly accessing system clipboard"

[neilcsmith-net]

Reverts #8462

Unfortunately looks like we might have to back this out of NB26 and also take more time to consider how to integrate this change into NB27. This currently causes a test failure because it routes copy through NbClipboard, but not paste. Setting clipboard contents in NbClipboard is asynchronous - getting contents from it waits for the setting task, but this is not happening because paste is bypassing it.

[mbien]

safer that way. Who knows what else doesn't expect the asynchronous nature of NbClipboard (#8476 the test didn't expect that at least)

[matthiasblaesing]

I will not intervene, but having a requested feature reverted, because a broken test fails feels wrong to me. Don't know when/if I will look into the problem, so feel free to merge, but I don't agree.

[neilcsmith-net]

@matthiasblaesing yes, it's unfortunate, but in my opinion the test is valid and the fix isn't correct at this point. We need to work out the right approach to take before your other PR with this is merged to master too.

[mbien]

the test failed because the behavior changed. Fixing the test is not the problem, I did that already. Its more about wanting to risk that something else fails due to that change or not. I am fairly neutral here but since this release has a few risky merges already I do prefer the revert slightly.

[ebarboni]

ok ok then merging. And if green I will cut the rc3