mipmap sizes need updating

[jdchristensen]

I realize that there are some technical issues preventing the docs from being updated, so I thought I should record this so it doesn't get lost. The list of mipmap sizes at

https://docs.darktable.org/lua/stable/lua.api.manual/types/dt_lua_image_t/#dt_lua_image_tgenerate_cache

is out of date. As far as I can see from the code, there is no "tiny" version anymore, and there are other differences too, even in 5.4.1. Also, in master, two new larger sizes are added.

master:

180, 360, 720, 1440, 1920, 2560, 4096, 5120, 6144, 7680

5.4.1:

180, 360, 720, 1440, 1920, 2560, 4096, 5120

Edit: Also, the docs should mention that these are the widths. They could also add the heights. The info is in src/common/mipmap_cache.c.