ProjectRoot

Finds the relative location of the project root.

Used in tests which rely on the working directory - unfortunately Intellij and sbt have different default working directories for executing tests from subprojects: while sbt defaults to the project root, intellij defaults to the subproject.

Previously a consistent behaviour was achieved by setting Test / baseDirectory := (ThisBuild / Test / run / baseDirectory).value, however that broke the bsp build within Intellij - it simply wouldn't recognise subprojects with this setting any more.