Some unpackers are misnamed about pillow

[Yay295]

This is related to #8019, because I wrote those packers in the correct order, which is actually the opposite of the unpackers.

[Yay295]

Here's the names they should be based on what they actually do and the format specified in Unpack.c.

Pillow/src/libImaging/Unpack.c

Lines 1534 to 1543 in 824db71

	/* raw mode syntax is "<mode>;<bits><flags>" where "bits" defaults
	depending on mode (1 for "1", 8 for "P" and "L", etc), and
	"flags" should be given in alphabetical order. if both bits
	and flags have their default values, the ; should be left out */
	/* flags: "I" inverted data; "R" reversed bit order; "B" big
	endian byte order (default is little endian); "L" line
	interleave, "S" signed, "F" floating point */
	/* exception: rawmodes "I" and "F" are always native endian byte order */

RGB;15 → XBGR;1555
RGB;16 → BGR;565
BGR;5 → XRGB;1555
BGR;15 → XRGB;1555
BGR;16 → RGB;565
RGB;4B → XBGR;4
RGBA;4B → ABGR;4
RGBA;15 → ARGB;1555
BGRA;15 → ABGR;1555

Unfortunately the specified format doesn't quite work because the bands in these modes aren't all the same size, so I just listed all of the sizes for those modes.

The good thing about listing out the band sizes though is that those names aren't already being used, so I could add all of them as "new" rawmodes and the old ones could be deprecated without interfering with one another.

[radarhere]

There's a slightly awkward overlap in code that would change with this and with #7965.

[Yay295]

Yes. This change would supersede both #7965 and #8019.

[Yay295]

I have a branch for these changes, but it's based on #8026 because it affects the same test file.

[radarhere]

That branch has now become #8158