Fix preloading when chunk group contains multiple chunks

[rtsao]

In some instances, chunks would not be preloaded when they should.

This would occur in a scenario like the following:

// main.js
import("./a.js");
import("./b.js");

// a.js
import shared from "./shared.js";
export default "a";

// b.js
import shared from "./shared.js";
export default "b";

// shared.js
export default "shared";

This would yield the following chunks (simplified naming)

• chunk-runtime.js
• chunk-vendor.js
• chunk-main.js
• chunk-a.js
• chunk-b.js
• chunk-shared.js

In webpack terminology, these chunks fit into three chunk groups:

• main group
  • chunk-runtime.js
  • chunk-vendor.js
  • chunk-main.js
• a group
  • chunk-a.js
  • chunk-shared.js
• b group
  • chunk-b.js
  • chunk-shared.js

The bug

chunk-shared.js would not be preloaded because the import()s for a.js and b.js would only be instrumented with the chunk ids for the chunk-a.js and chunk-b.js chunks, respectively.

A side effect of this meant that any translations in shared.js would be SSR'd, but would be missing on the initial client-side render because these translations would not be inlined into the SSR.

This PR ensures that chunk-shared.js is also added to the import promise instrumentation, ensuring that chunk-shared.js is preloaded correctly along with either chunk-a.js or chunk-b.js

[rtsao]

!merge

[old-fusion-bot[bot]]

Triggered Fusion.js build verification: https://buildkite.com/uberopensource/fusion-release-verification/builds/1661