Fix compilation of fields named 'bytes' or 'str' (#226)

* if you have a field named "bytes" using the bytes type, it doesn't work.
* Enable existing use-case & generalize solution to cover it

Co-authored-by: Spencer <spencer@sf-n.com>

tests/inputs/config.py

@@ -2,7 +2,6 @@
 # Remove from list when fixed.
 xfail = {
     "namespace_keywords",  # 70
-    "namespace_builtin_types",  # 53
     "googletypes_struct",  # 9
     "googletypes_value",  # 9
     "import_capitalized_package",