Reproduction steps:
1. Open the attached project “BugRepro”
2. Open the “Assets/Scenes/PlayMaJiang.unity” scene
3. Observe the Console Window

Expected result: Scripts can utilize {{Unity.PerformanceTesting;}} provided they are located within an Editor folder in a loosely organized project
Actual result: “error CS0234: The type or namespace name 'PerformanceTesting' does not exist in the namespace 'Unity' (are you missing an assembly reference?)”

Reproducible with: 2.8.0-preview, 3.0.0-pre.1, 3.0.3 (2021.3.40f1, 2022.3.37f1), 3.0.3 (6000.0.10f1)

Reproduced on: Windows 11 23H2 (22631.3007), Windows 10 (10.0.19045) 64bit (user’s)
Not reproduced on: No other environment tested