Rust: Proposed speedup 2.

Author: geoffw0

rust/ql/lib/codeql/files/FileSystem.qll

@@ -46,17 +46,17 @@ extensible predicate additionalExternalFile(string relativePath);
 /** A file. */
 class File extends Container, Impl::File {
   pragma[nomagic]
-  private predicate fromSource0() {
-    exists(ExtractorStep s | s.getAction() = "Extract" and s.getFile() = this)
+  string getRelativePath0() {
+    result = this.getRelativePath()
   }
 
   /**
    * Holds if this file was extracted from the source code of the target project
    * (rather than another location such as inside a dependency).
    */
   predicate fromSource() {
-    this.fromSource0() and
-    not additionalExternalFile(this.getRelativePath())
+    exists(ExtractorStep s | s.getAction() = "Extract" and s.getFile() = this) and
+    not additionalExternalFile(this.getRelativePath0())
   }
 
   /**