I *think* that the per-module configuration metadata that goes here should be per-developer, not tracked in git.
I decided which to keep and which to ignore by following advice given at <https://intellij-support.jetbrains.com/hc/en-us/articles/206544839> and <https://github.com/github/gitignore/blob/master/Global/JetBrains.gitignore>, which in turn influenced <https://www.gitignore.io/api/jetbrains>.