fix: strip BOM before calling transform hook

[TrickyPi]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:
resolves #5258

Description

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
rollup	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 23, 2023 0:07am

[github-actions]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#fix/xiaopi-bom

Notice: Ensure you have installed Rust nightly. If you haven't installed it yet, please first see https://www.rust-lang.org/tools/install to learn how to download Rustup and install Rust, then see https://rust-lang.github.io/rustup/concepts/channels.html to learn how to install Rust nightly.

or load it into the REPL:
https://rollup-959tpz9t0-rollup-js.vercel.app/repl/?pr=5268

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a083019) 98.87% compared to head (e8dc65c) 98.87%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5268   +/-   ##
=======================================
  Coverage   98.87%   98.87%           
=======================================
  Files         232      232           
  Lines        8945     8946    +1     
  Branches     2334     2334           
=======================================
+ Hits         8844     8845    +1     
  Misses         42       42           
  Partials       59       59           

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[lukastaegert]

Great work!

[github-actions]

This PR has been released as part of rollup@4.5.2. You can test it via npm install rollup.