🐛 Fix broken installation when upgrading from typer <0.12.0 to typer >=0.12.0, make typer independent of typer-slim, include typer command in typer package.

This would solve the issue #790

Current state as of 0.12.0

Since version 0.12.0, the typer pip installable package doesn't include the typer Python importable package/module, instead it declares it depends on the pip installable package typer-slim[standard], to include the standard extras.

And the pip installable package typer-slim is the one that provides the Python importable typer package/module.

But this is problematic for old installations, because of the way package managers handle them, they install typer-slim, including the typer directory with the code, then they remove the old typer package with its associated files, which means removing almost all the files in the typer directory, only leaving the new files since version 0.12.0.

In this PR

Now the pip installable typer includes all the dependencies in typer-slim, plus the dependencies defined in typer-slim[standard]. So, typer no longer depends on typer-slim. And the pip installable typer package includes the code, the Python importable package/module typer. Now typer includes the typer command.

And typer-slim includes the same, but without installing the optional dependencies by default, only including an optional dependencies group standard (with rich and shellingham).

Now typer-cli doesn't really do anything, it's there only for backwards compatibility, for a bit, for those that could have it as a dependency. Typer now includes the typer command.