[M108 Migration] Fix incorrect module dependancy

[M108 Migration] Fix incorrect module dependancy

Fixing dependency issue : `ui/` shouldn't depend on `content/`, which
may result in build breaks caused by not yet generated mojo files.

IMContentEfl which resides in ui layer had a direct dependancy on
content::RenderWidgetHostImpl, which is incorrect as per chromium
guidelines. Instead, introduce a public helper class as proxy to
route calls at content layer.

Reference: https://review.tizen.org/gerrit/285551

Change-Id: Ia1ecd29fc9badf58e89c997b6c081880de1c4f66
Signed-off-by: Gajendra N <gajendra.n@samsung.com>