Update version to 3.9.0

value_field_typeclass should be a enum module, not EnumDescriptor
object.

Also expanding tests for enum valued maps.

Fixes #4580
Signed-off-by: Sorah Fukumori <her@sorah.jp>

Remove unused fields

Down Integrate to GitHub

Enabling silent mode by default to reduce make compilation noise

[Ruby] Remove to_hash methods

Make the JSON util string output functions match the Message::SerializeToString() behavior.  This is helpful when packing the output into string fields of reused protobuf messages.

As a followup to ca3ead77, treat plugin executables as well as protoc as host tools.

Follow up on https://github.com/protocolbuffers/protobuf/pull/6221

This avoids hitting the following warning when including GPBDescriptor.h in ARC
projects with stricter warning settings:
error: 'assign' property of object type may become a dangling reference; consider using 'unsafe_unretained' [-Werror,-Wobjc-property-assign-on-object-type

We first hit this in XCode 11, it's unclear whether it simply got stricter about
enforcing this warning or whether the flags enabled with -Wall or -Weverything
have been expanded.

In some platforms ${CMAKE_INSTALL_LIBDIR} expands to `lib64`. The libraries
are correctly installed in that directory, but the RPATH is set to point to
`$ORIGIN/../lib`, where it should be `$ORIGIN/../lib64`.

Merge 3.8.x into master branch

The wire_format_lite_inl.h header file was made unnecessary in #5839
and deleted in #5921, so remove the comment about it.

Update CONTRIBUTING.md to clarify who should set the labels

Down integrate to GitHub

release notes: no

I'm getting `src/google/protobuf/map_field.cc(284): error C2899: typename cannot be used outside a template declaration`

removing `typename` fixes the issue

This fixes compatibility with bazel when passing `--incompatible_no_support_tools_in_action_inputs` which will be flipped in an upcoming release.

Update protobuf version to 3.8.0

Fix gulpfile to use gulp 4 API

Previously, foo_value and foo (wrapper field) will both have get/setFooValue