Use transposed size after opening for TIFF images

[radarhere]

Alternative to #8387

At the moment, load() might change the size of a TIFF image, since TIFF images are automatically transposed when doing so.

load() is a method that many users are probably not even aware of, and so they might find

from PIL import Image
im = Image.open("/Users/andrewmurray/pillow/Pillow/Tests/images/g4_orientation_5.tif")
print(im.size)  # (88, 590)
print(im.copy().size)  # (590, 88)

unexpected.

After this PR, the first im.size will also be (590, 88). This has means that changes from #6186 and #6190 can be removed.

#8387 solves this by making im.size sometimes different to im._size. I would like to avoid that, and have instead found a solution by adding TiffImageFile.load_prepare().

While we are here streamlining things so that an image does not change its size after loading, I've also updated ImageFile to remove an implication that loading might change an image's mode.

[homm]

Not sure how it affects multipage images with different page sizes

[radarhere]

When seeking to a different TIFF frame, self.im is populated afresh.

Pillow/src/PIL/TiffImagePlugin.py

Lines 1189 to 1198 in 08d9c89

	def seek(self, frame: int) -> None:
	"""Select a given frame as current image"""
	if not self._seek_check(frame):
	return
	self._seek(frame)
	# Create a new core image object on second and
	# subsequent frames in the image. Image may be
	# different size/mode.
	Image._decompression_bomb_check(self.size)
	self.im = Image.core.new(self.mode, self.size)

[homm]

Yeah, I saw this and tried to remove this initialization and relay on load_prepare instead, for some reasons it didn't work.

For me providing correct canvas (self.im) in the base class is more preferable than recreating it in the plugin. There was another approach which doesn't introduce difference between im.size and im._size.

[radarhere]

Ah, I see now - my load_prepare() would create a new core image when the image was loaded after seek().

I've pushed a commit following your other approach.