PYCBC-1828: Propagate OOM failures from init_pycbc_dict_keys

Changes
--------
* Change init_pycbc_dict_keys to return int, checking each of the
  ~130 interned dict-key globals and returning -1 on the first
  PyUnicode_FromString failure instead of leaving the global
  permanently null with no signal to the caller
* Update the pycbc_dict_keys.hxx/.cxx Jinja2 templates to match, and
  regenerate the bindings so the checked-in output stays in sync
* Check init_pycbc_dict_keys's return value in PyInit__core, failing
  module init cleanly (Py_DECREF(module); return nullptr) on the same
  pattern already used for cache_exception_classes and the other
  init steps, instead of silently continuing with null interned keys

Change-Id: I2919a3dbada81e6e79de1584eed7ce4f38b9aadf
Reviewed-on: https://review.couchbase.org/c/couchbase-python-client/+/250070
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>

Author: thejcfactor

src/module.cxx

@@ -180,7 +180,10 @@ PyInit__core(void)
     return nullptr;
   }
 
-  init_pycbc_dict_keys();
+  if (init_pycbc_dict_keys() < 0) {
+    Py_DECREF(module);
+    return nullptr;
+  }
 
   return module;
 }