ivi-shell: activate weston surface with a seat when left click or touch.

ivi-shell: activate weston surface with a seat when left click or touch.

Similar with Desktop shell, set activate to weston surface which is
left-clicked by pointer or touched. This is needed to focus it with a seat.
Without this, a feature who gets activated weston surface by using
weston_surface_get_main_surface doesn't work correctly because it can
not get correct focused weston surface. For example, input-panel uses
weston_surface_get_main_surface to get a weston surface. With this
weston surface, it get a member: output to decide which output shall
show a input-panel, software keyboard. Without activation,
input-panel-ivi can not find a correct output which shows e.g.
weston-editor who uses input-method.

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>