As the context's translate() is additive, there is no need for
the two consecutive calls of it inside _sceneFunc(): The same
effect can be achieved with with just one call of translate().
A corresponding update was done in the unit test for Text that
had a pair of calls to translate() in the expected call dump.
A small improvement to avoid re-testing the presence of underline
and line-through attributes in the textDecoration property on each
line of the text being rendered.
This is just a minor improvement (optimization) to _setTextData():
Flag shouldAddEllipsis is not changed inside the loop, thus no need
to recalculate the value of additionalWidth for every line of the
original text.
Similar to how it's handled in getWidth() and getHeight() of Konva.Text,
let _setTextData() treat undefined values of the 'width' and 'height'
attributes as if they are set to 'auto', not as if they are fixed.
