[klipper] Use full text for DBus return values

In a recent commit HistoryItem::text() became the visual representation
of the mimedata; often a truncated string.

mimeData()->text() always returns the full value.

BUG: 446441
2 jobs for !1249 with work/klipper_dbus in 9 minutes and 23 seconds (queued for 32 seconds)
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