[C++] Update the validator to skip structs in namespaces other than t…

…he current one. (#8324)

* [Python] Generate `.pyi` stub files when `--python-typing` is on.

To support this change, the following modifications were made:

-  added a new option to disable `numpy` helpers generation;
-  added a new flag to control the target Python version:

   `--python-version` can be one of the following:

   - `0.x.x` – compatible with any Python version;
   - `2.x.x` – compatible with Python 2;
   - `3.x.x` – compatible with Python 3.
-  added codegen utilities for Python;
-  added a note that the generated .py file is empty.

* [C++] Update the validator to skip structs in namespaces other than the current one.

src/idl_gen_cpp.cpp

@@ -470,7 +470,11 @@ class CppGenerator : public BaseGenerator {
 
           // Check that nativeName doesn't collide the name of another struct.
           for (const auto &other_struct_def : parser_.structs_.vec) {
-            if (other_struct_def == struct_def) { continue; }
+            if (other_struct_def == struct_def ||
+                other_struct_def->defined_namespace !=
+                    struct_def->defined_namespace) {
+              continue;
+            }
 
             auto other_name = Name(*other_struct_def);
             if (nativeName == other_name) {