Evas textblock: Use width of item format to position cursor.

Evas textblock: Use width of item format to position cursor.

Summary:
Use width of item format to position cursor.

Sometimes it becomes very difficult to
position cursor over item and selection
becomes very difficult as we position the
cursor once the input X coord reached end of the item,
like one attached in the test plan. So this patch
decides over 50% of item width for X coord reaches
to position it at start or end.

@ix

Test Plan:
Attached setup shows how difficult to position cursor at the end when clicked
over item and selection is also very difficult. Consider such case in mobile
device, its becomes impossible to position cursor at the end and selection is
too much difficult.

{F27036}

Also added test cases in evas test suite

Reviewers: herdsman, tasn

Subscribers: cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D3390

Change-Id: I801bfd2e3754299b5268be9970eed9ae5b340935