Allow float center for rotate operations

[radarhere]

In im.rotate(), there is

Pillow/src/PIL/Image.py

Lines 2375 to 2379 in 5bacce9

	if center is None:
	# FIXME These should be rounded to ints?
	rotn_center = (w / 2.0, h / 2.0)
	else:
	rotn_center = center

Looking through the code after that, there is no reason why they can't be floats - the numbers are simply combined with other floats.

Pillow/src/PIL/Image.py

Lines 2381 to 2399 in 5bacce9

	angle = -math.radians(angle)
	matrix = [
	round(math.cos(angle), 15),
	round(math.sin(angle), 15),
	0.0,
	round(-math.sin(angle), 15),
	round(math.cos(angle), 15),
	0.0,
	]
	def transform(x, y, matrix):
	(a, b, c, d, e, f) = matrix
	return a * x + b * y + c, d * x + e * y + f
	matrix[2], matrix[5] = transform(
	-rotn_center[0] - post_trans[0], -rotn_center[1] - post_trans[1], matrix
	)
	matrix[2] += rotn_center[0]
	matrix[5] += rotn_center[1]

This also allows the rotation center to be the exact center of an image with odd dimensions - although that also sound like a good argument why the user might want to pass in floats as the center, so I've updated the type hint accordingly.

[hugovk]

Only a seven-year-old FIXME :)