Auto merge of #125378 - lcnr:tracing-no-lines, r=oli-obk

remove tracing tree indent lines

This allows vscode to collapse nested spans without having to manually remove the indent lines. This is incredibly useful when logging the new solver. I don't mind making them optional depending on some environment flag if you prefer using indent lines

For a gist of the new output, see https://gist.github.com/lcnr/bb4360ddbc5cd4631f2fbc569057e5eb#file-example-output-L181

r? `@oli-obk`

Author: bors