Rollup merge of rust-lang#141405 - RalfJung:GetUserProfileDirectoryW, r=ChrisDenton

GetUserProfileDirectoryW is now documented to always store the size

Update to match MicrosoftDocs/sdk-api#1810

Also fix a bug in the Miri implementation while I am starting at that code...

r? ```@ChrisDenton```
Fixes rust-lang#141254

Author: matthiaskrgr

std/src/sys/pal/windows/os.rs

@@ -202,8 +202,6 @@ fn home_dir_crt() -> Option<PathBuf> {
             |buf, mut sz| {
                 // GetUserProfileDirectoryW does not quite use the usual protocol for
                 // negotiating the buffer size, so we have to translate.
-                // FIXME(#141254): We rely on the *undocumented* property that this function will
-                // always set the size, not just on failure.
                 match c::GetUserProfileDirectoryW(
                     ptr::without_provenance_mut(CURRENT_PROCESS_TOKEN),
                     buf,