[ts] Mark compiled JS as auto-generated and binary to filter from GitHub
[ts] Mark compiled JS as auto-generated and binary to filter from GitHub

This marks the contents of package `build` directories as auto-generated so that changes to these files are collapsed but visible (if expanded) in GitHub PRs, helping reviewers focus on salient changes.

Test plan: put up a PR that makes changes to `build` and ensure the built JS is collapsed by default and still expandable.

exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent