<text> behavior with writing-mode:sideways-lr

[tkent-google]

https://svgwg.org/svg2-draft/text.html#WritingModeProperty
https://svgwg.org/svg2-draft/text.html#TextLayoutAlgorithm

The algorithm looks not to take into account of writing-mode: sideways-lr. Text should grow up from current text position in the sideways-lr writing mode, but the algorithm assumes text always grows down if horizontal flag is false.

For example,
5.2.2.4.6

6. For each index k in the range [i,j]:
   1. Add shift to the x coordinate of the position in result[k], if the "horizontal" flag is true, and to the y coordinate otherwise.

"Add" here should be "subtract" for sideways-lr writing mode.