Fix persistent tooltip in the "new folder" input of the file picker

When a new folder is tried to be created in the file picker dialog a
tooltip is shown on the input if the folder name exists already.
However, this tooltip was not cleared, so it was still shown even if the
name was fixed, the folder was created and then the "New folder" input
was shown again.

Now the tooltip is cleared as soon as the input changes, as keeping it
shown in that case did not provide any benefit either (and it is
consistent with how the "new folder" input works in the Files app view).

The input is also cleared whenever the menu that shows the input is
opened again, as otherwise the tooltip would be still shown if the menu
was closed and opened again without changing the input (and the menu
could be opened again after changing to another directory where the new
folder name is no longer duplicated).

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>