Add canonicalization to source & use paths (#421)

Also added file path print to FileNotFound error

crates/nu-protocol/src/ast/import_pattern.rs

@@ -24,6 +24,17 @@ pub struct ImportPattern {
 }
 
 impl ImportPattern {
+    pub fn new() -> Self {
+        ImportPattern {
+            head: ImportPatternHead {
+                name: vec![],
+                span: Span::unknown(),
+            },
+            members: vec![],
+            hidden: HashSet::new(),
+        }
+    }
+
     pub fn span(&self) -> Span {
         let mut spans = vec![self.head.span];
 
@@ -50,3 +61,9 @@ impl ImportPattern {
         }
     }
 }
+
+impl Default for ImportPattern {
+    fn default() -> Self {
+        Self::new()
+    }
+}