Auto merge of #19511 - DonatJR:implement-read-methods-on-filereadersync, r=jdm

Implement read methods on FileReaderSync

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Implemented the read methods on the FileReaderSync struct according to https://w3c.github.io/FileAPI/#dfn-FileReaderSync

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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 fix #15114

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- [x] There are tests for these changes

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