[M108 Migration] Support callback for customer app error page.

[M108 Migration] Support callback for customer app error page.

Currently WebBrowser load customer error page with below apis:
  callback "load,error"
  ewk_view_html_string_load
  ewk_view_html_string_override_current_entry_load
With these, it cannot meet all case in WebBrowser.
Customer Error Page will be stored as an independent entry.
It will cause issues related with navigation back/forward or reload.

Implement ewk_view_error_page_load_callback_set for app.
Interpose on the stage of NavigationThrottleEfl::WillFailRequest.
And pass customer error page in here.

For this implementation, customer error page will not store in navigation entry.

Currently, this change is supported for WebBrowser.

Reference:
- https://review.tizen.org/gerrit/279699/

Change-Id: I5dd1ac7bbac95b2c3456c35dbe569cf231aafef4
Signed-off-by: feifei08.liu <feifei08.liu@samsung.com>