Edje, Elementary: Remove <password=off> tag when password mode is disabled

Edje, Elementary: Remove <password=off> tag when password mode is disabled

Summary:
When edje_password_show_last option is enabled, the edje_entry uses <password=off>
for showing last character. But, when password mode is disabled by the elm_entry,
<password=off> is remained in the text. It can cause some problems.

Because, there is no way to control password mode by API for the edje_entry.
The elm_entry can't remove <password=off> tag before getting text from the edje_entry.
So, the patch adds edje_object_part_text_hide_visible_password() function and
the elm_entry will use this when elm_layout_theme_apply() is called.
@fix

Test Plan:
1. Run "elementary_test".
2. Show "Entry Password" demo. (Newly added by this patch)
3. Password mode is enabled. Put some text.
4. Click "Show Password" check box to disable password mode.
5. Put more text.
6. Click "Hide Password" check box to enable password mode again.
7. See a character among the text is visible. (without this patch)

Reviewers: tasn, herdsman, cedric, jpeg, thiepha, raster

Reviewed By: raster

Subscribers: Blackmole, z-wony, woohyun

Differential Revision: https://phab.enlightenment.org/D3988

Change-Id: I622ecdfa3ed5fafe15a6085cc86f5538a5ca1b6e