Function read_source_file 

pub fn read_source_file(path: &Path) -> FileReadResult

Read a source file, detecting binary files that should emit TS1490.

TypeScript detects binary files by checking for:

• UTF-16 BOM (FE FF for BE, FF FE for LE)
• Non-valid UTF-8 sequences
• Many control bytes (not expected in source files)
• Files with many null bytes