tests/edje: add comprehensive edje reloading test

Summary:
this verifies:

• successfully loading a file
• emission of "load" signal when performing a file load
• swallowing an object
• no-op of file load operation on same file if mtime is unchanged
• successfully reloading the same file if the mtime has changed
• preserving user-defined data across file reloads

Depends on D9877

Reviewers: cedric

Reviewed By: cedric

Subscribers: reviewers, committers

Tags: efl

Differential Revision: https://phab.enlightenment.org/D9878