Turbopack: normalize ref type for external tracing (#78226)
Fixes duplicate `CachedExternalModule`s, due to different result depending on the reference type:
As opposed to adding the whole reference type to the external's `AssetIdent`, normalize the reference type, tracing an external with `EcmaScriptModules(ImportPart(Evaluation))` (which returns nothing for side-effect-free packages) is strange anyway.
```
request: "@emotion/react"
reference_type: EcmaScriptModules(ImportPart(Evaluation))
tracing_resolve_result: []
tracing_resolve_affecting: ["[project]/node_modules/.pnpm/@emotion+react@11.11.1_@types+react@19.1.1_react@19.2.0-canary-1d6c8168-20250411/node_modules/@emotion/react/package.json", "[project]/node_modules/@emotion/react"]
```
```
request: "@emotion/react"
reference_type: EcmaScriptModules(ImportPart(Export("CacheProvider")))
tracing_resolve_result: ["[project]/node_modules/.pnpm/@emotion+react@11.11.1_@types+react@19.1.1_react@19.2.0-canary-1d6c8168-20250411/node_modules/@emotion/react/dist/emotion-react.cjs.mjs [externals-tracing] (ecmascript)"]
tracing_resolve_affecting: ["[project]/node_modules/.pnpm/@emotion+react@11.11.1_@types+react@19.1.1_react@19.2.0-canary-1d6c8168-20250411/node_modules/@emotion/react/package.json", "[project]/node_modules/@emotion/react"]
```
