Salsify the crate graph

I.e. make it not one giant input but multiple, for incrementality and decreased memory usage for Salsa 3 reasons.

crates/intern/src/symbol.rs

@@ -42,6 +42,18 @@ struct TaggedArcPtr {
 unsafe impl Send for TaggedArcPtr {}
 unsafe impl Sync for TaggedArcPtr {}
 
+impl Ord for TaggedArcPtr {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.as_str().cmp(other.as_str())
+    }
+}
+
+impl PartialOrd for TaggedArcPtr {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
 impl TaggedArcPtr {
     const BOOL_BITS: usize = true as usize;
 
@@ -113,7 +125,7 @@ impl TaggedArcPtr {
     }
 }
 
-#[derive(PartialEq, Eq, Hash)]
+#[derive(PartialEq, Eq, Hash, PartialOrd, Ord)]
 pub struct Symbol {
     repr: TaggedArcPtr,
 }