VS Code keeps the case. I.e. it  correctly replaces
even getWorkspaceFolders.

The only places where we didn't replace the string were when
we were using the VS Code API (vscode.workspace.workspaceFolders).

If the integration test workspace is missing, fail the test instantly.
This improves contributor experience preventing
unrelated integration test failures.
This commit also moves the documentation for running integration tests
to a more prominent position in the docs.

We migrated to TS and introduced new concepts since the last update.

This change introduces Jest test framework to run our unit tests.

Implementing integration and unit tests using mocha and adding two
documents that describe the testing strategy and guide how to write
new tests.