Allow Views Submission Links to work with ctools dropdown

Problem/Motivation

webform_handler_field_submission_link doesn't render the same way as views_handler_field_node_link and therefor can't be used with the dropdown links views_handler_field_ctools_dropdown field handler

Steps to reproduce

Add a view with a
Webform submissions: View link or
Webform submissions: Edit link or
Webform submissions: Delete link
Then add a Global: Dropdown links with one or all of the links above.
The result is they don't show (because they don't generate a last_render_text in views_handler_field_links::get_links used by views_handler_field_ctools_dropdown)

Proposed resolution

Change them to work like views_handler_field_node_link instead of using the l() to render the links

Remaining tasks

User interface changes

API changes

Data model changes