Support ttb multiline text

[radarhere]

Resolves #4945

Currently,

from PIL import ImageFont, ImageDraw, Image

im = Image.new("RGB", (200, 200), "white")
draw = ImageDraw.Draw(im)
font = ImageFont.truetype("Tests/fonts/DejaVuSans/DejaVuSans.ttf", 24)
draw.text((100, 10), "abc\n123\nXYZ", "black", font, direction="ttb")
im.show()

gives

ValueError: ttb direction is unsupported for multiline text

This PR would instead generate

[hugovk]

@nulano How does this look?