[RDY] Extract line_consumption.c from misc1.c

This pull request extracts some functions that are concerned with physical line consumption of a buffer on screen from `misc1.c` and puts it in a file called `screenline.c`. (See #209)
I forgot that we should include here all headers which contain types of parameters of functions in `screenline.h.generated.h`. `"nvim/buffer_defs.h"` for `win_T`, `<stdbool.h>` for `bool` and `"nvim/vim.h"` for `linenr_T` (though `linenr_T` will be moved to `"nvim/pos.h"` in #941)