Configure TypeScript to use source files during test and development time #174
Description
Due to these lines in tsconfig.packages.json, TypeScript is supposed to use sources instead of build files at development and test time. In other words, changes in package A should be available to its consumer package B without rebuilding package A. This is not currently the case, as both the VS Code language server and our tests fail to use the sources directly without building them. We should fix this.