Add support for seekdir(). #4488

Job	Run time
Rustfmt	11s
Check nightly-only targets (nightly)	21s
Check --no-default-features (nightly)	56s
Check selected Tier 3 platforms (nightly)	33s
Check (stable)	2m 9s
Test (ubuntu)	42s
Check (nightly)	2m 10s
Test use-libc (ubuntu)	46s
Test (ubuntu-20.04)	47s
Check (1.63)	2m 16s
Test use-libc (i686-linux)	44s
Test (i686-linux)	55s
Test use-libc (aarch64-linux)	52s
Test (aarch64-linux)	57s
Test use-libc (powerpc64le-linux)	51s
Test (powerpc64le-linux)	57s
Test (riscv64-linux)	55s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 2s
Test use-libc (riscv64-linux)	51s
Test rustix_use_experimental_asm (s390x-linux)	1m 0s
Test use-libc (s390x-linux)	51s
Test (s390x-linux)	56s
Test use-libc (arm-linux)	36s
Test (arm-linux)	56s
Test (ubuntu-stable)	44s
Test (i686-linux-stable)	56s
Test (aarch64-linux-stable)	56s
Test (riscv64-linux-stable)	55s
Test (s390x-linux-stable)	56s
Test (powerpc64le-linux-stable)	55s
Test (arm-linux-stable)	58s
Test (ubuntu-1.63)	55s
Test (i686-linux-1.63)	57s
Test (aarch64-linux-1.63)	54s
Test (riscv64-linux-1.63)	55s
Test (s390x-linux-1.63)	51s
Test (powerpc64le-linux-1.63)	53s
Test (arm-linux-1.63)	53s
Test (macos-latest)	38s
Test (macos-13)	49s
Test (windows)	37s
Test (windows-2019)	43s
Test (musl)	43s
	39m 22s

Provide feedback