Add rewritePathSegment to Folder::Resolve

Author: asgerf

shared/util/codeql/util/FileSystem.qll

@@ -267,6 +267,15 @@ module Make<InputSig Input> {
        * - Complex patterns like `foo-*.txt` are also supported
        */
       default predicate allowGlobs() { none() }
+
+      /**
+       * Gets an alternative path segment to try if `segment` did not match a child.
+       *
+       * The motivating use-case is to map compiler-generated file names back to their sources files,
+       * for example, `foo.min.js` could be mapped to `foo.ts`.
+       */
+      bindingset[segment]
+      default string rewritePathSegment(string segment) { none() }
     }
 
     /**
@@ -317,9 +326,13 @@ module Make<InputSig Input> {
           segment = ".." and
           result = current.getParentContainer()
           or
-          isOptionalPathComponent(segment) and
           not exists(getChild(current, segment)) and
-          result = current
+          (
+            isOptionalPathComponent(segment) and
+            result = current
+            or
+            result = getChild(current, rewritePathSegment(segment))
+          )
           or
           allowGlobs() and
           (