Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/40373

When copying some text from another note and paste,
it goes through `copy_as_gfm` `paste` handler
that calls `e.preventDefault()` which stops things.
But then when inserting the text, we manually trigger
an `input` event with jQuery which doesn't seem to be
picked up by Vue `v-model`.

Using copy/paste trick from https://stackoverflow.com/a/41046276/796832