Replace regex package module checks with actual code checks (#55824)
Fixes https://github.com/JuliaLang/julia/issues/55792
Replaces https://github.com/JuliaLang/julia/pull/55822
Improves what https://github.com/JuliaLang/julia/pull/51635 was trying
to do
i.e.
```
ERROR: LoadError: `using/import Printf` outside of a Module detected. Importing a package outside of a module is not allowed during package precompilation.
```