As a developer, I want to create a Theia extension that extends VS Code API

[kavitha-subr]

This issue is related to #11
I want to capture terminal contents using the Theia extension and extend VS Code API to exploit this capability.

Note: Currently, Theia also does not support capturing the terminal contents directly, and a feature request has been raised here eclipse-theia/theia#13085
So, we would like to mock the implementation for now and return a static string as the terminal content.