Combine common and tests

[inancgumus]

I propose combining the code and tests and restructuring the extension code.

One of the reasons:
The current package structure makes it hard to get coverage for the project.

Although we test the types in the common/ package to some extent, the coverage tool cannot cover them. This is because the tests are in tests/ while their tests are in common/. To do that, we need to use -coverpkg all the time.

This problem makes our jobs more complicated to create new tests and see what we are improving.

[mstoykov]

I would expect this is because the tests are in another package and by default coverage is only tracked for the package under test which is what -coverpkg is for.

You can see how it's used in k6 here so that it also tracks coverage for all (k6) packages that are dependencies of the package under test.

[inancgumus]

Thanks, right, but I don't see a good reason for these super-related packages and their tests are in different packages.

go test ./tests ./common \
    -coverpkg=github.com/grafana/xk6-browser/common,github.com/grafana/xk6-browser/tests \
    -coverprofile=cover.out