* fix json_format.ParseDict modifies input

* added unit test

* fix naming

* Fix parsing empty Struct Values from Json

This fixes a bug. When parsing a struct from JSON like
    struct = json_format.Parse('{"k": {}}', Struct())
then the struct's "k" value would end up not initialized, and accessing
the value would raise an error.
    In[1]: struct['k']
    ValueError: Value not set
That seems to be because the Struct field of the Value was not set.
    In[2]: struct
    Out[2]:
    fields {
      key: "k"
      value {
      }
    }

This commit makes sure that the Value's Struct field is initialized even
if the Struct has no values itself.

This commit also extends a test to cover this case.

* Additionally test for empty list

* ParseFromString returns bytes parsed

ParseFromString is documented as returning the number of bytes parsed,
and the C++ implementation does this, so the Python implementation
should too.

See #5165.

* Fix docstring

* Add a test for ParseFromString length behavior

Many classes within collections were moved to collections.abc in Python
3.3 -- their usage as imported directly from collections is now
deprecated as of Python 3.7 and will be removed soon.

The fallback import added in this PR can be removed entirely when
support for versions of Python prior to 3.3 is dropped.

* _SURROGATE_PATTERN check for ucs4
Skip some test for ucs2 by sys.maxunicode

1. Fix C++ tests.
  * Add missing files to Makefile.am and fix distcheck in tests.sh
  * Remove BUILT_SOURCES from conformance/Makefile.am.
  * Add some missing override keyword.
  * Add a type cast to int64 because our StrCat() in stubs can't handle size_t.
2. Fix Java tests.
  * Add missing test dependency on guava in pom.xml.
  * Include newly referenced test data in test resources.
  * Manually fix map_lite_test.proto which is overwritten because it's mapped
    from map_test.proto in google3.
  * Add back "optimize_for = LITE_RUNTIME" which is still needed to keep the
    opensource test passing as it's still running lite tests.
  * Add a type cast in newBuilder() because without it the code doesn't compile
    with openjdk javac 1.8 (the compiler can't figure if it's the right type
    due to complex generic typing).
3. Fix Python tests.
  * Remove/replace references to <hash_map>.
  * Suppress more warnings in setup.py.
  * Replace incorrect header inclusion for google/protobuf/proto_api.h.
  * Add strings::EndsWith to google/protobuf/stubs/strutil.h because it's
    referenced in the updated python C extension code.
  * Replace proto2 with google::protobuf. The proto2 name is leaked to
    opensource because we removed the subsitition rule for proto2 namespace
    but only fixed C++ source code and forgot to update python C extension code.

Compilation of Python wrappers fails with Python 3.7 because
the Python folks changed their C API such that
PyUnicode_AsUTF8AndSize() now returns a const char* rather
than a char*. Add a patch to work around. Relates #4086.

* Update message_module.cc

Add missing piece from pull request #4698:  actually initialize the new API object.

* Update message_module.cc

Internal convert file was broken. Change the capsule to the correct name

The compiler and util subpackages are created by the build_py class in
setup.py. This has caused an issue in the protobuf package in
conda-forge (https://github.com/conda-forge/protobuf-feedstock/issues/40),
which is fixed by this commit.

* Fix setup.py for windows build.

* Bump version number to 3.5.2

* Cat the test-suite.log on errors for presubits

* Cython's stack does not have .py file name. Only check filenames when end with .py for _CalledFromGeneratedFile()

Add _file_desc_by_toplevel_extension back for compatibility issue with 3.4.1.

_file_desc_by_toplevel_extension is a temporary solution for FieldDescriptor.file.
FieldDescriptor.file was added in code gen. However, we need to keep it for some time for compatibility reason (with 3.4.1 only). May try to remove it after 2 years.

Hi!
Sorry for bothering with such a minor thing, but I just noticed and fixed one annoying typo in WKT's test suite:
`"accpets" -> "accepts"`

Thanks!