Allow stdin like with Bash in Python mode

[philipturner]

Swift-Colab uses the Python pexpect library to interact with running processes. This lets it extract colorized, interactive output - a feature not present in google/swift-jupyter. However, this means it will freeze when the process requests input.

In the image above, the third %system command requests permission to overwrite a file.

There is currently no mechanism to pass input into a running process. The Python Jupyter kernel passes input in, so it is theoretically possible. But this feature will take a non-negligible amount of time to implement. I am deferring its addition to a future release.

[philipturner]

Patched and being implemented in Swift-Colab v2.3. I switched from pexpect to a reimplementation of the terminal in googlecolab/colabtools. Colorized output appears when building a Swift package that generates compiler warnings, so the new implementation is a go.