Introduce -m/--module flag to execute a `main` function in a package (#52103)
This aims to bring similar functionality to Julia as the `-m` flag for
Python which exists to directly run some function in a package and being
able to pass arguments to that function.
While in Python, `python -m package args` runs the file
`<package>.__main__.py`, the equivalent Julia command (`julia -m Package
args`) instead runs `<Package>.main(args)`. The package is assumed to be
installed in the environment `julia` is run in.
An example usage could be:
Add the package:
```julia
(@v1.11) pkg> add https://github.com/KristofferC/Rot13.jl
Cloning git-repo `https://github.com/KristofferC/Rot13.jl`
Updating git-repo `https://github.com/KristofferC/Rot13.jl`
Resolving package versions...
Updating `~/.julia/environments/v1.11/Project.toml`
[43ef800a] + Rot13 v0.1.0 `https://github.com/KristofferC/Rot13.jl#master`
Updating `~/.julia/environments/v1.11/Manifest.toml`
[43ef800a] + Rot13 v0.1.0 `https://github.com/KristofferC/Rot13.jl#master`
```
And then it can be run (since it has a `main` function) via:
```
❯ ./julia/julia -m Rot13 "encrypt this for me" "and this as well"
rapelcg guvf sbe zr
naq guvf nf jryy
```
I'm not sure if `-m/--module` is the best choice but perhaps the
association to Python makes it worth it.