feat: add opus filetype to assets & mime types

[mia-riezebos]

Description

the web is using the opus codec more and more for audio streaming, to mentally separate these from ogg:vorbis, some people use the .opus file extension. I wanted to do this for a project of mine as well, and figured i'd add it to the main vite repo.

Additional context

mostly concerned about whether ive used the mrmime part correctly to add opus?

this failed 1 test that seems unrelated (building on windows might be the culprit), see below:

 RUN  v0.29.7 C:/Users/mia/libraries/side-projects/vite

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⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Failed Tests 1 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 FAIL  playground/preserve-symlinks/__tests__/preserve-symlinks.spec.ts > not-preserve-symlinks
AssertionError: expected '' to be 'hello vite' // Object.is equality
 ❯ playground/preserve-symlinks/__tests__/preserve-symlinks.spec.ts:11:43
      9| 
     10| test('not-preserve-symlinks', async () => {
     11|   expect(await page.textContent('#root')).toBe('hello vite')
       |                                           ^
     12| })
     13| 

  - Expected   "hello vite"
  + Received   ""

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯[1/1]⎯

 Test Files  1 failed | 56 passed | 10 skipped (67)
      Tests  1 failed | 508 passed | 91 skipped (600)
   Start at  03:11:26
   Duration  87.90s (transform 12.33s, setup 108.59s, collect 25.26s, tests 389.36s)

 ELIFECYCLE  Command failed with exit code 1.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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