Baggage part 1/3: change propagator signatures (#6157)

## Summary of changes

First of multiple PRs to add OpenTelemetry baggage support.

This PR prepares propagators to support baggage. Since all propagators are currently _trace_ propagators and work on `SpanContext`, this PR changes all propagator signatures to accept or return a new `PropationContext` instead. `PropationContext` is a light container for both the existing `SpanContext` and the new `Baggage` type.

Baggage progpation across services is _not_ implemented in this PR.

## Reason for change

Adding support for OpenTelemetry baggage.

## Implementation details

- Add `Baggage` class
- Add `PropagationContext`, which contains `SpanContext` and `Baggage`
- Modify all propagator signatures (and usages) to replace `SpanContext` with `PropagationContext`

## Test coverage

- added unit tests for `Baggage` (get, set, remove, etc)
- existing propagators are already covered by extensive tests

## Other details
<!-- Fixes #{issue} -->

<!--  ⚠️ Note: where possible, please obtain 2 approvals prior to merging. Unless CODEOWNERS specifies otherwise, for external teams it is typically best to have one review from a team member, and one review from apm-dotnet. Trivial changes do not require 2 reviews. -->

tracer/src/Datadog.Trace.Coverage.collector/CoverageCollector.cs

@@ -301,13 +301,15 @@ private void ProcessFolder(string folder, SearchOption searchOption)
             _logger?.Warning($"Processed {numAssemblies} assemblies in folder: {folder}");
 
             // The following is just a best effort approach to indicate in the test session that
-            // we sucessfully instrumented all assemblies to collect code coverage.
+            // we successfully instrumented all assemblies to collect code coverage.
             // Is not part of the spec but useful for support tickets.
             // We try to extract session variables (from out of process sessions)
             // and try to send a message to the IPC server for setting the test.code_coverage.injected tag.
-            if (SpanContextPropagator.Instance.Extract(
-                    EnvironmentHelpers.GetEnvironmentVariables(),
-                    new DictionaryGetterAndSetter(DictionaryGetterAndSetter.EnvironmentVariableKeyProcessor)) is { } sessionContext)
+            var extractedContext = SpanContextPropagator.Instance.Extract(
+                EnvironmentHelpers.GetEnvironmentVariables(),
+                new DictionaryGetterAndSetter(DictionaryGetterAndSetter.EnvironmentVariableKeyProcessor));
+
+            if (extractedContext.SpanContext is { } sessionContext)
             {
                 try
                 {
@@ -323,7 +325,7 @@ private void ProcessFolder(string folder, SearchOption searchOption)
             }
             else
             {
-                _logger?.Debug($"CoverageCollector.Test session context cannot be found, skipping IPC client and sending injection tags");
+                _logger?.Debug("CoverageCollector.Test session context cannot be found, skipping IPC client and sending injection tags");
             }
         }
 

tracer/src/Datadog.Trace/AspNet/TracingHttpModule.cs

@@ -132,14 +132,15 @@ private void OnBeginRequest(object sender, EventArgs eventArgs)
                 HttpRequest httpRequest = httpContext.Request;
                 var requestHeaders = RequestDataHelper.GetHeaders(httpRequest) ?? new System.Collections.Specialized.NameValueCollection();
                 NameValueHeadersCollection? headers = null;
-                SpanContext propagatedContext = null;
+                PropagationContext extractedContext = default;
+
                 if (tracer.InternalActiveScope == null)
                 {
                     try
                     {
                         // extract propagated http headers
                         headers = requestHeaders.Wrap();
-                        propagatedContext = SpanContextPropagator.Instance.Extract(headers.Value);
+                        extractedContext = SpanContextPropagator.Instance.Extract(headers.Value).MergeBaggageInto(Baggage.Current);
                     }
                     catch (Exception ex)
                     {
@@ -152,7 +153,7 @@ private void OnBeginRequest(object sender, EventArgs eventArgs)
                 string httpMethod = httpRequest.HttpMethod.ToUpperInvariant();
                 string url = httpContext.Request.GetUrlForSpan(tracer.TracerManager.QueryStringManager);
                 var tags = new WebTags();
-                scope = tracer.StartActiveInternal(_requestOperationName, propagatedContext, tags: tags);
+                scope = tracer.StartActiveInternal(_requestOperationName, extractedContext.SpanContext, tags: tags);
                 // Leave resourceName blank for now - we'll update it in OnEndRequest
                 scope.Span.DecorateWebServerSpan(resourceName: null, httpMethod, host, url, userAgent, tags);
                 if (headers is not null)
@@ -172,7 +173,8 @@ private void OnBeginRequest(object sender, EventArgs eventArgs)
                 // (e.g. WCF being hosted in IIS)
                 if (HttpRuntime.UsingIntegratedPipeline)
                 {
-                    SpanContextPropagator.Instance.Inject(scope.Span.Context, requestHeaders.Wrap());
+                    var injectedContext = new PropagationContext(scope.Span.Context, Baggage.Current);
+                    SpanContextPropagator.Instance.Inject(injectedContext, requestHeaders.Wrap());
                 }
 
                 httpContext.Items[_httpContextScopeKey] = scope;