WXT should bundle multiple `background.js` scripts like it does with `content.js`

Feature Request

Currently it is easy to modularize the content scripts in the entrypoints folder by simply appending .content.ts to the file name.

Add the same ability to background.js.

Is your feature request related to a bug?

N/A

What are the alternatives?

From @aaronklinker-st :

For now, a quick fix to using multiple background scripts is to use Vite's glob import:

// background/index.ts
const scripts = import.meta.glob<{ default: () => void }>('./*.background.ts', { eager: true });

export default defineBackground(() => {
  Object.values(scripts).map(script => script.default.main());
});

Then put your other files in like background/some-name.background.ts

Additional context

https://discord.com/channels/1212416027611365476/1290896813850886197

Start by tracing how WXT discovers and bundles modular content scripts in the entrypoints folder, then compare that path with background script handling. Done means multiple files using the background naming convention are bundled and usable like the existing content scripts, with coverage for the new behavior.