Refactor Bluetooth error handling
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Replace the error messages with an enum in `net/bluetooth_thread.rs`. Rename `bluetooth_blacklist.rs` to `bluetooth_utils.rs` and put the error conversion in it.
With this the returned errors in DOM classes follow the specification.
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because there is no Web Bluetooth test API implementation yet.
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