Delete grpc-native-core from master, along with all references

[murgatroid99]

I also copied some .proto files that were being referenced from the submodule into test/proto.

Output of git grep -- -core:

README.md:Directory: [`packages/grpc-native-core`](https://github.com/grpc/grpc-node/tree/[email protected]/packages/grpc-native-core) (lives in the `[email protected]` branch) (see here for installation information)
packages/grpc-native-core/README.md:The `grpc` npm pacakge previously lived in this package. It has been removed. It now lives in the [`[email protected]` branch](https://github.com/grpc/grpc-node/tree/grpc%401.24.x/packages/grpc-native-core) where bugfixes are still being applied.

In the test directory tests that test all combinations of client and server from both libraries, I removed only the set that uses both the client and server from the native library, and I switched to installing the native library from npm instead of using the local copy. This way, we can still test that grpc-js matches the behavior of grpc, and I think the interop tests should still work.

After/in parallel to this, I think I can easily migrate the grpc-tools build to a GitHub Workflow and remove the Kokoro build tests entirely. I would also like to migrate the regular tests to a GitHub Workflow, but there doesn't seem to currently be a good way to get the per-test reports that we currently have.

[murgatroid99]

It is expected that the Electron build jobs fail, because I deleted those config files and build scripts.

[murgatroid99]

The Windows Build Job has been failing due to an issue that is fixed in #1422. That is probably the reason it is failing here.

The Mac build job config files were also deleted so I expect that to fail too.

[merlinnot]

My offer still stands 🙂 #1170

[murgatroid99]

@merlinnot Do you know how to get good per-test output comparable to what we currently get from Kokoro from GitHub Actions?

[merlinnot]

That looks similar to GitHub annotations. I personally only used that for ESLint before, to annotate errors and warnings, but it looks like people are also using it for failed tests:

Did I understand your intention correctly, to have an output with failures only?

[murgatroid99]

Yes, that looks like what I'm looking for: separate reports for each test failure, along with specific output from each test. I found mocha-github-actions-reporter which probably does that, though I'm not entirely sure how it's used.