fix(python): duplicated kwargs when field is multi-inherited (#2654)

When a struct field is inherited from more than one parent (this could
be twice from the same type - in the case of a diamond shape; or from
two distinct parents that declare the same field), the lifted keyword
arguments in python would be duplicated for this field.

This is because the method that performs the keyword argument lifting
did not perform name-based de-duplication, and operates directly on the
"raw" assembly (whereby it must traverse the inheritance tree itself,
as opposed to the Go generator which uses `jsii-reflect` and has the
field collection done by that library).

Fixes #2653

packages/jsii-pacmak/lib/targets/python.ts

@@ -513,8 +513,8 @@ abstract class BaseMethod implements PythonBase {
     // resolved, so build up a list of all of the prop names so we can check against
     // them later.
     const liftedPropNames = new Set<string>();
-    if (this.liftedProp?.properties?.length ?? 0 >= 1) {
-      for (const prop of this.liftedProp!.properties!) {
+    if (this.liftedProp?.properties != null) {
+      for (const prop of this.liftedProp.properties) {
         liftedPropNames.add(toPythonParameterName(prop.name));
       }
     }
@@ -751,24 +751,36 @@ abstract class BaseMethod implements PythonBase {
     const liftedProperties: spec.Property[] = [];
 
     const stack = [this.liftedProp];
-    let current = stack.shift();
-    while (current !== undefined) {
+    const knownIfaces = new Set<string>();
+    const knownProps = new Set<string>();
+    for (
+      let current = stack.shift();
+      current != null;
+      current = stack.shift()
+    ) {
+      knownIfaces.add(current.fqn);
+
       // Add any interfaces that this interface depends on, to the list.
       if (current.interfaces !== undefined) {
-        stack.push(
-          ...current.interfaces.map(
-            (ifc) => resolver.dereference(ifc) as spec.InterfaceType,
-          ),
-        );
+        for (const iface of current.interfaces) {
+          if (knownIfaces.has(iface)) {
+            continue;
+          }
+          stack.push(resolver.dereference(iface) as spec.InterfaceType);
+          knownIfaces.add(iface);
+        }
       }
 
       // Add all of the properties of this interface to our list of properties.
       if (current.properties !== undefined) {
-        liftedProperties.push(...current.properties);
+        for (const prop of current.properties) {
+          if (knownProps.has(prop.name)) {
+            continue;
+          }
+          liftedProperties.push(prop);
+          knownProps.add(prop.name);
+        }
       }
-
-      // Finally, grab our next item.
-      current = stack.shift();
     }
 
     return liftedProperties;