Add layer to module trace (#50851)

## What?

Adds `layer` to the traces for `build-module-x`, will allow us to figure
out in what layer the module was compiled, as you can now get multiple
for the same module.

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packages/next/src/build/webpack/plugins/profiling-plugin.ts

@@ -180,6 +180,7 @@ export class ProfilingPlugin {
             span = parentSpan.traceChild(spanName)
           }
           span.setAttribute('name', module.userRequest)
+          span.setAttribute('layer', module.layer)
           moduleSpans!.set(module, span)
         })