Rust: Add extracted files to summary stats.

rust/ql/src/queries/summary/SummaryStats.ql

@@ -11,6 +11,8 @@ import Stats
 
 from string key, string value
 where
+  key = "Extracted files" and value = count(File f | exists(f.getRelativePath())).toString()
+  or
   key = "Lines of code" and value = getLinesOfCode().toString()
   or
   key = "Lines of user code" and value = getLinesOfUserCode().toString()

rust/ql/test/query-tests/diagnostics/SummaryStats.expected

@@ -1,2 +1,3 @@
+| Extracted files | 6 |
 | Lines of code | 24 |
 | Lines of user code | 24 |