[3.1] Support large EventSource filter args

[noahfalk]

Port #27500 to 3.1

Customer Impact

Today APM tools such as ApplicationInsights ask customers to reference NuGet packages and load in-proc assemblies in order to make distributed tracing work. When an engineer needs to diagnose a production issue and the application developer didn't have the foresight to adopt an appropriate NuGet package already, it is extremely high friction to retroactively add it. It requires source access, rebuilding the application, redeploy to production, and restarting the running instance where the problem is reproing. DiagnosticSourceEventSource and EventPipe provide an alternate telemetry channel that can be enabled on-demand with no restart and no redeploy to solve the same class of issues. The fix here removes a rough edge allowing the alternative EventPipe scenario to work much more effectively for this use case.

How the fix works

Going one level deeper, DiagnosticSourceEventSource requires the telemetry consuming tool to specify a list of runtime events to gather as well as every desired property on those events. This list could easily include dozens of events with multiple properties on each event when trying to use it for distributed tracing. Currently there is a limitation that the complete textual encoding of this list is less than 1KB and it is very easy to exceed this limit for this use case. If the limit is exceeded the runtime ignores the request and logs nothing. The fix relaxes this limit.

Testing

I have privately debugged and tested the fix using a prototype distributed tracing tool.

Risk

Low - ETW blocks tools from entering this codepath with more than 1KB of data so it can only be hit with new EventPipe based tooling. The modified code path is also wrapped in a blanket try/catch region such that even the previous bad behavior of throwing a NullReferenceException was silently ignored and the application continued as if the problematic logging request had never been made.

Original commit text

1. Fix NullReferenceException. When the filter args exceeded the
   hard-coded size limit GetDataFromController would return data = null.
   The code previously asserted that data was not null and triggered NRE
   when it was. The fix correctly null checks the value instead of
   asserting and uses an empty args dictionary in this case, the same as if
   filter args had been empty to begin with.

2. ETW has always limited filter args to 1024 bytes but EventPipe has no
   such restriction. When using DiagnosticSourceEventSource it can be
   useful to specify a larger filter arg blob. I can't do anything about
   ETW's restriction but there is no need for the runtime to force
   EventPipe to be equally limited. The larger size also reduces the chance
   that we need to hit the fallback path above causing filter args to be
   ignored.

[danmoseley]

Please get a code review before merging 😃

[danmoseley]

Appears to be faithful port of https://github.com/dotnet/coreclr/pull/27500/files