feat[test]: add more example contracts (#4500)

add more example contracts from third party sources to increase
compiler coverage, and our ability to detect compilation faults on
"in-the-wild" source code.

currently, the contracts are just tested for compilations, although in
the future we could add some integration / unit tests with them.

Author: charles-cooper

tests/functional/examples/thirdparty/__init__.py

@@ -0,0 +1 @@
+# third party contracts, check that they compile