Add option to view's exposed filter to show only published terms (even to users who have access to unpublished terms)

Attached patch. Needs tests.

> If this is implemented, I'd argue that the default setting should be for "Show published terms only" to be set to true/checked.

I agree with you, but AFAIK usually default options need to be backwards compatible/produce the same results than before, So probably we are not gonna do that.

The last submitted patch, 8: 3108322-hide-unpublished-terms-8.patch, failed testing. View results →

Inspired from #8 and #9, I have created a patch which provide "Show published terms only" to be set to true/checked.
I have tested this patch in view exposed filter and its working properly.

The last submitted patch, 11: 3108322-show-only-published-terms-11.patch, failed testing. View results →