Add test case for MainDialog Activity

[FlyingPumba]

This PR adds an Espresso test case for the MainDialog Activity. It also includes three auxiliary classes with two custom Matchers and one custom ViewAction.

The test case was automatically generated using the ETG tool, which aims to achieve high activity coverage. In particular, this Espresso test increases the current overall coverage in the project by 20.38%.

Although this contribution was automatically generated, the code in this PR was manually reviewed to ensure it adheres to standard contribution guidelines.