Fix mmap with offset on Windows

query allocation granularity (64k on Windows, larger than page size which is 4k),
ensure offset to MapViewOfFile is a multiple of the granularity

add a test for mmap with offset
fix szfile and szarray values

replace 0xffffffff with typemax(Uint32)
add a test with a larger offset than 64k
use div(a, b) instead of ifloor(a/b)
add extra error message info from Windows API
Merge pull request #7242 from tkelman/mmap_windows

Fix mmap_array with offset on Windows