internal: Don't rely on FxHashSet order

Previously, SCIP generation would iterate over all the external
symbols by calling `.difference()` on an FxHashSet and iterating over
them. If any tokens had a moniker but no definition, the loop would
terminate early.

AFAICS this code is unreachable today (all the monikers also have
definitions), but the code is clearly wrong. Ensure we process all
tokens regardless of the order.

Author: Wilfred

crates/rust-analyzer/src/cli/scip.rs

@@ -237,7 +237,7 @@ impl flags::Scip {
             let token = si.tokens.get(id).unwrap();
 
             let Some(definition) = token.definition else {
-                break;
+                continue;
             };
 
             let file_id = definition.file_id;