Use MochaJS's best practices

[andyleejordan]

Prerequisites

• I have written a descriptive issue title.
• I have searched all issues to ensure it has not already been reported.

Summary

• Convert from TDD to BDD which use describe() and it() instead of suite() and test().
• The use of lambdas for unit tests is also discouraged because it prevents the use of Mocha's test context.
• Moreover, we have a number of tests which use foreach loops that should instead be parameterized tests.
• I introduced a ensureExtensionIsActivated utility method, but we also need an ensureEditorServicesIsConnected utility method to reduce the flakiness of the new debugger test, and it should use a hook-level timeout when waiting for the connection.
• Enable --enable-source-maps since we use transpiled TypeScript. Not possible again because the tests first launch Code, a Node app.

Proposed Design

N/A

[andyleejordan]

Oh THIS is what I was working on @rjmholt 😅

[andyleejordan]

Resolved by #3643.