Make swift and obj-c patterns Python3 compatible

[changusmc]

Fixes an issue that causes the stone generation to blow up when running in Python3.

SwiftyDropbox/stone/stone/backends/swift_types.py", line 238, in _determine_validator_type
Dec  2 18:05:18.716: [10:05:18]: ▸ pat = pat.encode('unicode_escape').replace("\"", "\\\"") if pat else pat
Dec  2 18:05:18.716: [10:05:18]: ▸ TypeError: a bytes-like object is required, not 'str'

Checklist

General Contributing

• Have you read the Code of Conduct and signed the CLA? Didn't sign CLA, I'm a Dropbox employee

Is This a Code Change?

• Non-code related change (markdown/git settings etc)
• Code Change
• Example/Test Code Change

Validation

• Have you ran tox?
• Do the tests pass?
  They don't pass locally, but they seem to fail on a main checkout as well.

____________________________________ TestGeneratedPythonTypes.test_namespace_comments _____________________________________

self = <test.test_python_types.TestGeneratedPythonTypes testMethod=test_namespace_comments>

    def test_namespace_comments(self):
        # type: () -> None
        ns = ApiNamespace('files')
>       ns.add_doc("Test Doc testing a :type:`Type`.")

test/test_python_types.py:66:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = ApiNamespace('files'), docstring = 'Test Doc testing a :type:`Type`.'

    def add_doc(self, docstring):
        # type: (six.text_type) -> None
        """Adds a docstring for this namespace.

        The input docstring is normalized to have no leading whitespace and
        no trailing whitespace except for a newline at the end.

        If a docstring already exists, the new normalized docstring is appended
        to the end of the existing one with two newlines separating them.
        """
>       assert isinstance(docstring, six.text_type), type(docstring)
E       AssertionError: <type 'str'>

stone/ir/api.py:132: AssertionError
========================================== 1 failed, 161 passed in 34.37 seconds ==========================================
ERROR: InvocationError for command /Users/changd/dev/stone/.tox/codecov/bin/coverage run --rcfile=.coveragerc -m pytest (exited with code 1)```

[codecov]

Codecov Report

Merging #203 (a4efd21) into main (0b49b05) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #203      +/-   ##
==========================================
- Coverage   51.73%   51.72%   -0.02%     
==========================================
  Files          37       37              
  Lines        8367     8369       +2     
  Branches     1786     1786              
==========================================
  Hits         4329     4329              
- Misses       3724     3726       +2     
  Partials      314      314              

Flag	Coverage Δ
unit	51.72% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
stone/backends/obj_c_types.py	0.00% <0.00%> (ø)
stone/backends/swift_types.py	0.00% <0.00%> (ø)

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