RoslynEx: Generated .editorconfig contains duplicates

[PostSharpBot]

Seen when building the Caravela TestApp. The generated file is attached.

[PostSharpBot]

The ticket was imported from TP-29498.
Original creator: a***n [at] postsharp.net
Original creation time: 2021-11-18T13:31:39Z
Original severity: Cosmetical
Original business value: Lowest
Original source: Internal