Summary:
Values different from numbers and percentages should be ignored
and the default values should be applied (zeros).
And set the min and max of the offset value to be 0, 1.
Also, this patch make that the offset is not input in the reverse order.
Test Plan:
Test SVG Image
```
<svg viewBox="0 0 200 200" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" >
<linearGradient id="grad" x1="0" y1="0" x2="1" y2="1">
<stop offset="10%" stop-color="white"/>
<stop offset="0.2" stop-color="red"/>
<stop offset="30% k" stop-color="blue"/>
<stop offset="40%" stop-color="yellow"/>
<stop offset="0.5m" stop-color="red"/>
<stop offset="0.6 " stop-color="green"/>
<stop offset="70%m" stop-color="black"/>
<stop offset="80%" stop-color="white"/>
</linearGradient>
<rect x="20" y="20" width="160" height="160" fill="url(#grad)"/>
</svg>
```
Result
{F4792365}
Reviewers: Hermet, raster, kimcinoo
Reviewed By: Hermet
Subscribers: cedric, #reviewers, #committers
Tags: #efl
Differential Revision: https://phab.enlightenment.org/D12318