Change imports to ES modules, specify function input types and add
non-null assertions (! at the end of the expression) to make the type
checker pass.

Use export keyword instead of specifying all the exports at the end of
file (CommonJS)

We exit the openers early if there is no workspaceFolder. On top of
that, we added one assertion for the project API response being present.

We changed imports and exports to ES modules. We had to specify all
function input types and types of class properties. We added many
non-null assertions to make the type checker pass.

We changed GitLabJob to RestJob to match the naming convention and used
it in the status_bar.

We introduced `asMock` helper that prevents us from having to always
type cast the mock with `as jest.Mock`.

fix: ci variables links are broken

See merge request !215

refactor: convert status_bar to TypeScript

See merge request !224

docs: introduce minimum supported version

See merge request !221