API errors now return information via gRPC metadata (not the response)

[dmondrik]

What does this Pull Request accomplish?

API errors are now returned as part of gRPC metadata rather than as part of the response. This is more natural for gRPC.

• The approach relies on custom methods that are per resource type, since in at least some cases the message comes dynamically from the resource handle (session).
  • Ideally the names of those methods could be simple and rely on parameter overloading to resolve the difference. However, XNET has 2 resources types that are both 32-bit integers. Therefore the simplest solution is to include the resource type name as part of the method name.
• The methods should be hand maintained because many of them require a fallback process. In MI for example, it returns the last error code for the session as well as the description. However, that may not be the status code we wanted to look up (that can happen if 2 threads are called in parallel and both fail with different status codes.)
  • In that case, such drivers have a different method of looking up a static error message for a given error code. The name and signature of that fallback method varies greatly.

Why should this Pull Request be merged?

Task 2103382: Change generated code to return UNKNOWN on error status.

What testing has been done?

I built locally. I have not run any tests manually but I am expecting they will run as part of this PR.

[SparkingSpork]

Approving based on CMakeLists changes and deferring to others on the code generation/API changes.

[reckenro]

Looks like there's four integration tests (run as part of build_desktop part of CI) expecting errors that'll need to be updated to fit the new expectations:

NiFakeNonIviServiceTests.InitWithReturnedSessionFailsInit_AccessSession_SessionIsNotInMapAndStatusValueIsReturned
NiFakeNonIviServiceTests.GetStringAsReturnedValueReturnsNull_ReturnsErrorAndEmptryString
NiFakeNonIviServiceTests.InitWithError_CallsGetLatestErrorAndReturnsMessage
NiFakeServiceTests.NiFakeService_FunctionCallErrors_ResponseValuesNotSet

I'm expecting a good bit of System tests to start failing too that expect and check errors (run after a successful build_desktop action is run).

[dmondrik]

Looks like there's four integration tests (run as part of build_desktop part of CI) expecting errors that'll need to be updated to fit the new expectations:

NiFakeNonIviServiceTests.InitWithReturnedSessionFailsInit_AccessSession_SessionIsNotInMapAndStatusValueIsReturned NiFakeNonIviServiceTests.GetStringAsReturnedValueReturnsNull_ReturnsErrorAndEmptryString NiFakeNonIviServiceTests.InitWithError_CallsGetLatestErrorAndReturnsMessage NiFakeServiceTests.NiFakeService_FunctionCallErrors_ResponseValuesNotSet

I'm expecting a good bit of System tests to start failing too that expect and check errors (run after a successful build_desktop action is run).

I'll be waiting for that now that I've fixed up the unit tests.