How to reproduce:
1. Open the attached project's Scene labeled "SampleScene"
2. Open the Profiler (Window -> Analysis -> Profiler)
3. In the Profiler window, enable the 'Deep Profile' option
4. Enter the Play Mode
5. Inspect the performance on 'Scripts'
6. Pause the recording
7. Search for 'AnimatorOverrideController.SendNotification'

Expected result: SendNotification doesn't take a significant amount of time
Actual result: There's a ~4ms delay for each Animator

Reproducible with: 2019.4.29f1, 2020.3.15f1, 2021.1.16f1, 2021.2.0b6, 2022.1.0a4

Link to forums: https://forum.unity.com/threads/animatorcontrolleroverride-applyoverrides-way-too-expensive.522573/