refactor(package): split cargo_package to modules (#14982)

### What does this PR try to resolve?

Do nothing but move code around

* `cargo_package.rs` -> `cargo_package/mod.rs`
* Extract vcs info helpers to `cargo_package/vcs.rs`
* Extract verification helpers to `cargo_package/verify.rs`

Doing so because I realized how big `cargo_package.rs` has grown.
Like, the vcs helpers will continue growing with #14981 and potentially
other optimizations.

### How should we test and review this PR?

All tests pass.