Evas textblock: Use a common thickness and position at a underline.

Evas textblock: Use a common thickness and position at a underline.

Summary:
If a underline is drawn with seperated thickness and position, it doesn't look good.
It will take the thickest and the lowest underline.

@feature

Test Plan:
Set the following markup text in Evas Textblock.
<underline=on underline_color=#fff><font_size=20>Markup text <font_size=50>with</font_size> underline tag</font_size></underline>

It shows the underline is split to 3 underlines with different thickness and positions.
Commonly, underline has to be drawn with same thickness ans position per each line.

Reviewers: woohyun, herdsman, tasn

Reviewed By: tasn

Subscribers: jpeg, raster, subodh6129, cedric

Differential Revision: https://phab.enlightenment.org/D2971

Change-Id: I2c3a0cbfc03a29501f7e3878fa84934173430233