fix $env.FILE_PWD and $env.CURRENT_FILE inside overlay use (#15126)

# Description
Fixes: #14540
The change is similar to #14101

User input can be a directory, in this case, we need to use the return
value of find_in_dirs_env carefully, so in case, I renamed
maybe_file_path to maybe_file_path_or_dir to emphasize it.

# User-Facing Changes
NaN

# Tests + Formatting
Added 2 test cases

# After Submitting

tests/overlays/mod.rs

@@ -1,4 +1,4 @@
-use nu_test_support::fs::Stub::FileWithContentToBeTrimmed;
+use nu_test_support::fs::Stub::{FileWithContent, FileWithContentToBeTrimmed};
 use nu_test_support::playground::Playground;
 use nu_test_support::{nu, nu_repl_code};
 use pretty_assertions::assert_eq;
@@ -1408,3 +1408,50 @@ fn overlay_help_no_error() {
     let actual = nu!("overlay use -h");
     assert!(actual.err.is_empty());
 }
+
+#[test]
+fn test_overlay_use_with_printing_file_pwd() {
+    Playground::setup("use_with_printing_file_pwd", |dirs, nu| {
+        let file = dirs.test().join("foo").join("mod.nu");
+        nu.mkdir("foo").with_files(&[FileWithContent(
+            file.as_os_str().to_str().unwrap(),
+            r#"
+                export-env {
+                    print $env.FILE_PWD
+                }
+            "#,
+        )]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            "overlay use foo"
+        );
+
+        assert_eq!(actual.out, dirs.test().join("foo").to_string_lossy());
+    });
+}
+
+#[test]
+fn test_overlay_use_with_printing_current_file() {
+    Playground::setup("use_with_printing_current_file", |dirs, nu| {
+        let file = dirs.test().join("foo").join("mod.nu");
+        nu.mkdir("foo").with_files(&[FileWithContent(
+            file.as_os_str().to_str().unwrap(),
+            r#"
+                export-env {
+                    print $env.CURRENT_FILE
+                }
+            "#,
+        )]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            "overlay use foo"
+        );
+
+        assert_eq!(
+            actual.out,
+            dirs.test().join("foo").join("mod.nu").to_string_lossy()
+        );
+    });
+}