feat: simplify code that writes output files and add EOL at EOF

[marcusrbrown]

I consolidated the code that writes output files into a function that:

1. Converts the output data to a string using JSON.stringify
2. Ensures the directory path of the output file exists
3. Adds EOL to the end of the output data, to ensure all files are terminated with whitespace

The addition of EOL is to be consistent and avoid issues with downstream tools that have issues without EOL. There is likely an off-the-shelf package that can do detection, but os.EOL should cover Windows and everything else using \n.

[marcusrbrown]

I noticed a few issues with this change so I'll convert to draft for now:

• Extra newline from "Amalgamate" step don't add EOL at EOF if it's already there
• Similar pattern is used in resolve.ts move the utility code to a separate file