Add type annotations

[aleksslitvinovs]

Py-TestUI mostly doesn't have type annotations. This does not affect the framework's functionality but makes the source code less traceable and the user experience less pleasant since there are no IDE suggestions.

This issue will require changes in all project files therefore it would make sense to split it up by files.

[mihhail-m]

Type annotations can be generated, although not yet perfectly, but still would require less manual labor.
Linking this SO answer for more information: Automatic Type Annotations

[ruzv]

Annotating str, int, and other basic types can be done and IMO should be done. But there are a few blockers blocking annotation of Py-TestUI's core functionality - methods that use Py-TestUI classes.
The blockers are:

• import cycle with TestUIDriver and Elements. Both classes use each other and have methods that return instances of each other. This can be avoided circular imports in python, but something to keep in mind.
• NewDriver underlying web driver can be of different types for example appium driver or selenium remote driver. The blocker is a bit deeper in Elements that uses NewDriver to locate elements. Appium driver implements additional element location techniques like find_element_by_accessibility_id and find_element_by_android_uiautomator to base location techniques implemented by selenium remote web driver. Hence calling find_element_by_accessibility_id with the selenium web driver will result in a runtime error. This error might deserve its own issue, but either way, it blocks annotating Elements.