fix(path): avoid chdir() when resolving path (#28799)

Use uv_fs_realpath() instead.

It seems that uv_fs_realpath() has some problems on non-Linux platforms:
- macOS and other BSDs: this function will fail with UV_ELOOP if more
  than 32 symlinks are found while resolving the given path.  This limit
  is hardcoded and cannot be sidestepped.
- Windows: while this function works in the common case, there are a
  number of corner cases where it doesn't:
  - Paths in ramdisk volumes created by tools which sidestep the Volume
    Manager (such as ImDisk) cannot be resolved.
  - Inconsistent casing when using drive letters.
  - Resolved path bypasses subst'd drives.

Ref: https://docs.libuv.org/en/v1.x/fs.html#c.uv_fs_realpath

I don't know if the old implementation that uses uv_chdir() and uv_cwd()
also suffers from the same problems.
- For the ELOOP case, chdir() seems to have the same limitations.
- On Windows, Vim doesn't use anything like chdir() either. It uses
  _wfullpath(), while libuv uses GetFinalPathNameByHandleW().

src/nvim/eval/funcs.c

@@ -6479,7 +6479,7 @@ static void f_resolve(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   char *v = os_resolve_shortcut(fname);
   if (v == NULL) {
     if (os_is_reparse_point_include(fname)) {
-      v = os_realpath(fname, v);
+      v = os_realpath(fname, NULL, MAXPATHL + 1);
     }
   }
   rettv->vval.v_string = (v == NULL ? xstrdup(fname) : v);
@@ -6631,7 +6631,7 @@ static void f_resolve(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     xfree(buf);
   }
 # else
-  char *v = os_realpath(fname, NULL);
+  char *v = os_realpath(fname, NULL, MAXPATHL + 1);
   rettv->vval.v_string = v == NULL ? xstrdup(fname) : v;
 # endif
 #endif