Consume closure library from HEAD

[pcj]

This PR is a draft, it's not been tested thoroughly outside of an internal repository but I am using this PR commit successfully there.

• Remove //closure/library and consume closure library labels from https://github.com/google/closure-library now that the upstream has BUILD files. A large patch file is included to suppress errors in strict mode.
• Update com_google_template_soy and com_google_template_soy_jssrc to newer versions
• Update com_google_protobuf_js to 3.18.1
• Update closure compiler to v20200830. I could not move further without triggering compile errors in JSLibraryChecker (IIRC)
• Reverts #491
• Buildifier lint fixes

The patch of closure library sources is excessive and was done quickly via:

$ bazel query @com_google_javascript_closure_library//closure/goog/... > labels.txt

And then iteratively recompiling, adding suppressions via:

$ cat labels.txt | xargs buildozer -types closure_js_library 'add suppress JSC_DEPRECATED_CLASS_REASON'

A more targeted buildozer script would be preferable.

A few manual changes were made also such as https://github.com/google/closure-library/issues/1147.