Convert Flask path-injection sanitizer to MaD

I confirmed that without this sanitizer a test fails.

Author: owen-mc

python/ql/lib/semmle/python/frameworks/Flask.model.yml

@@ -0,0 +1,6 @@
+extensions:
+  - addsTo:
+      pack: codeql/python-all
+      extensible: barrierModel
+    data:
+      - ['flask', 'Member[send_from_directory].Argument[1,filename:]', 'path-injection']

python/ql/lib/semmle/python/frameworks/Flask.qll

@@ -631,17 +631,6 @@ module Flask {
     }
   }
 
-  /**
-   * To exclude `filename` argument to `flask.send_from_directory` as a path-injection sink.
-   */
-  private class FlaskSendFromDirectoryCallFilenameSanitizer extends PathInjection::Sanitizer {
-    FlaskSendFromDirectoryCallFilenameSanitizer() {
-      this = any(FlaskSendFromDirectoryCall c).getArg(1)
-      or
-      this = any(FlaskSendFromDirectoryCall c).getArgByName("filename")
-    }
-  }
-
   /**
    * A call to `flask.send_file`.
    *

python/ql/lib/semmle/python/security/dataflow/PathInjectionCustomizations.qll

@@ -98,4 +98,11 @@ module PathInjection {
 
   /** DEPRECATED: Use ConstCompareAsSanitizerGuard instead. */
   deprecated class StringConstCompareAsSanitizerGuard = ConstCompareAsSanitizerGuard;
+
+  /**
+   * A sanitizer defined via models-as-data with kind "path-injection".
+   */
+  class SanitizerFromModel extends Sanitizer {
+    SanitizerFromModel() { ModelOutput::barrierNode(this, "path-injection") }
+  }
 }