Simplify SelectionControllerEfl::OnMouseMove

Simplify SelectionControllerEfl::OnMouseMove

By passing the SelectionHandleEfl object as a parameter
instead of its type, we can greatly simplify this method.

For instance, patch factors out the magnifier positioning
logic out of the switch, now that it is common for all 3
types of handles.

Additionally, now two cases in the 'switch' statement can be
colapsed (ones that handle HANDLE_TYPE_LEFT and RIGHT).

Last, patch also moves the declaration of the
local variables within the scope they are needed.

Original beta/m42 patch:
- http://165.213.202.130/gerrit/#/c/85428/ , reviewed by
Janusz Majnert, Arnaud Renevier.

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=14304

Reviewed by: Janusz Majnert

Change-Id: Ie1b8a105e155e54e33e267d1ba70243a57234bd5
Signed-off-by: Antonio Gomes <a1.gomes@samsung.com>