This fixes a bug that was introduced in Select2 4.0.0 and only
partially fixed in Select2 4.0.6-rc.0 where the `title` attribute
that is set on the selection container (or individual selections,
for a multiple select) is not cleared when the text/title of the
option is not set. In most cases, users no longer see this issue
because the `text` property of most data objects is set, so the
`title` attribute will always be cleared correctly. There was a bug
for cases where the `text` property was not set, or where the `text`
property was set to an empty string, that resulted in the `title`
attribute persisting with the incorrect value.
We have fixed this issue by always removing the `title` attribute
from the selection (or not adding it in the first place, for a
multiple select) when the `text` and `title` properties of the data
object are empty or not present.
This also adds in a series of tests to ensure the `title` attribute
is set properly in a variety of cases, building upon the ones that
already existed.
Fixes#3895
efbfd14414