Rollup merge of #88647 - ChrisDenton:win-symlink-docs, r=joshtriplett
Rollup merge of #88647 - ChrisDenton:win-symlink-docs, r=joshtriplett

Document when to use Windows' `symlink_dir` vs. `symlink_file`

It was previously unclear why there are two functions and when they should be used.

Fixes: #88635

graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust