tree-wide: include sys/stat.h where necessary

tree-wide: include sys/stat.h where necessary

These source files uses symbols provided by sys/stat.h, e.g. struct stat,
S_IFREG, S_IFBLK, and so on. Let's explicitly include sys/stat.h where
necessary.

Glibc's fcntl.h includes bits/stat.h, which provides these symbols, so
these symbols can be used without explicitly including sys/stat.h. But,
based on the discussion in #37922, we should explicitly include relevant
headers, and should not rely on the indirect inclusion.

Similar to 4f18ff2e29b8054f30b084abcabf5f689f4b340b, but for sys/stat.h.