fix(core): Export spanToTraceContext function from span utils (#10364)

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Closes #10362

Author: kammeph

packages/core/src/index.ts

@@ -87,6 +87,7 @@ export {
   spanToTraceHeader,
   spanToJSON,
   spanIsSampled,
+  spanToTraceContext,
 } from './utils/spanUtils';
 export { getRootSpan } from './utils/getRootSpan';
 export { applySdkMetadata } from './utils/sdkMetadata';