Properly isolate tests from the Gradle user home When running Gradle, we use the current working directory as the base directory for searching a `settings.gradle` file. For tooling API tests this working directory is the one of Gradle itself, which causes a number of issues because the root directory of the project doesn't match the working directory.
Therefore, Gradle finds the `settings.gradle` file of its own build, instead of finding the one in the test.
As a workaround, TAPI tests now use an action which will set the working directory to the test directory, which should cover most cases. Additional cases like missing settings files in projects under tests have to be handled separately, as demonstrated in this commit for the ProjectBuilder test.