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

Down integrate to GitHub

Cherrypick 014872a9 to fix build

This reverts commit a7180caf.

This reverts commit 783971e8.
Revert an accidental revert!

This reverts commit 6d96493b.

This reverts commit c40018e5.

Update performance.md

Even though I just proofread this file, I noticed one more thing that needed correcting, which I fixed. The word "genereated" had to be corrected to "generated". My apologies for missing this on the initial check.

Down Integrate to GitHub

Update performance.md

I corrected a few grammatical mistakes and increased the document's readability by easing the language flow.

Update instruction on how to use JavaLite runtime

Fix typo 'pythong'

Typo fix for conformance test runner.