Checks if the element identified by locator is visible.
Returns true if it's visible; returns false if otherwise.

*Example:*
| ${isVisible}= | `Is Element Visible` | css=foo bar |

=>

| ${isVisible} = False   # or ${isVisible} = True

The value can be evaluated to run another keyword. 
i.e.  

| `EL Run Keyword If`    |  $[var('isVisible') eq true]   | My Keyword  |