ref(tracing): Sync baggage data in Http and envelope headers

[Lms24]

This PR is the continuation of our efforts of propagating baggage data along outgoing Http Requests and to Relay in envelope headers. It syncs the content of the trace envelope header with the baggage Http header we propagate with outgoing requests. This means that both headers will from now on have the same baggage contents (the envelope header has additional fields that are not part of Baggage).

This also means that from now on, the trace envelope header conforms with the immutability requirements set on baggage. Both headers will call Span.getBaggage() to get the baggage data. This method in turn checks if it is allowed to add values to the baggage (see #5205 for more details`). If it is, it will gather all values that are available at that time and mark baggage immutable for potential future calls. This ensures that both headers will get the same data and send consistent data to the next SDK (via outgoing requests) and Relay.

ref: https://getsentry.atlassian.net/browse/WEB-937

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.35 KB (added)
@sentry/browser - ES5 CDN Bundle (minified)	59.85 KB (added)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.15 KB (added)
@sentry/browser - ES6 CDN Bundle (minified)	53.49 KB (added)
@sentry/browser - Webpack (gzipped + minified)	19.92 KB (added)
@sentry/browser - Webpack (minified)	64.85 KB (added)
@sentry/react - Webpack (gzipped + minified)	19.95 KB (added)
@sentry/nextjs Client - Webpack (gzipped + minified)	43.9 KB (added)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.52 KB (added)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.04 KB (added)

[Lms24]

I wonder if line 508 is a problem. I thought that contexts could hold arbitrary data 🤔

[AbhiPrasad]

Yup contexts can hold arbitrary data!

[Lms24]

So this line shouldn't exist, right? I checked and it was added in #5171 to normalize trace context data but IIUC what's going on here, we're accidentally erasing all other contexts except the ones we're adding back (which is why I added line 510).

[Lms24]

Removed the line for the time being in eebeb6b (happy to revisit this if it's a problem). I checked, the other elements in normalized.contexts are normalized a few lines above:

sentry-javascript/packages/core/src/baseclient.ts

Lines 492 to 494 in eebeb6b

	...(event.contexts && {
	contexts: normalize(event.contexts, depth, maxBreadth),
	}),

[lobsterkatie]

We have that one for trace because of

sentry-javascript/packages/core/src/baseclient.ts

Lines 500 to 506 in 3a938aa

	// event.contexts.trace stores information about a Transaction. Similarly,
	// event.spans[] stores information about child Spans. Given that a
	// Transaction is conceptually a Span, normalization should apply to both
	// Transactions and Spans consistently.
	// For now the decision is to skip normalization of Transactions and Spans,
	// so this block overwrites the normalized event to add back the original
	// Transaction information prior to normalization.

.

That said, perhaps it's time to rethink that.

[lobsterkatie]

A few small questions/suggestions, but otherwise looks good!

[AbhiPrasad]

As was indicated in #5171 (comment), this will fix #5261 as per the comment here: #5261 (comment)