Account for fractional pixels when performing percentage transformations.

### Issue
When specifying transformations in terms of percentages, fractional pixel values are rounded when computing the transformation value. This can result in rounding errors, specifying manifesting itself in `moon.SimplePicker` when set to a large enough index for the rounding errors to compound.

### Fix
A temporary fix involves setting the corrected value based on a one-time measurement of the control width, when rendered. This minimizes the amount of unwanted animation from the initial picker value to the currently specified index, but there can still be a slightly noticeable shift. To fully eliminate this shift, we need to set the transformation before rendering, either via percentage as was originally implemented, or pre-computing the pixel amount, which requires a post-render measurement in this case.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>