Add Dir::{read_link_contents,symlink_contents} methods #1662

Job	Run time
Rustfmt	17s
Check Cross-Compilation on Rust nightly on Windows (nightly)	1m 33s
Check Cross-Compilation on Rust nightly (nightly)	1m 57s
Check Cross-Compilation on Windows (stable)	1m 42s
Check Cross-Compilation (stable)	1m 43s
Check Cross-Compilation on Windows (beta)	1m 24s
Check Cross-Compilation (beta)	1m 35s
Test (stable)	34s
Test with Rust nightly (ubuntu)	37s
Test (windows-latest)	4m 9s
Test with Rust nightly (windows)	1m 32s
Test (windows-2019)	2m 16s
Fuzz Targets	1m 6s
Test (macos-latest)	59s
Test (macos-11)	1m 10s
Test linux-raw support (ubuntu)	33s
Test linux-raw support (ubuntu-20.04)	29s
Test (beta)	30s
Test (msrv)	2m 29s
Test (ubuntu-20.04)	46s
Test on Musl (ubuntu)	50s
Test (aarch64-ubuntu)	2m 48s
	30m 59s

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