Use more natual way to run diff lastest items.
Infact, when we do compare on recent two clipboard item,
e.g.
first time copy => copy1
second time copy => copy2
Then, when invoke compare command use global key, copy1 passed
as second arg, and copy2 passed as first arg.
I consider reverse order is more natually.
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The filter expression is not really needed in this case.
https://github.com/hluk/CopyQ/issues/1284#issuecomment-617090264
diff_lastest_items
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