Small patch to force Unity to use MSAA in the scene view. Requires that a quality level with MSAA is active (set under Project Settings->Quality). Tested with the built-in and universal render pipelines in Unity 2022.3.50f1 and 6000.2.0a10.993.
This patch uses the "Detour" method where several internal unity functions are overwritten in memory with a jump instruction, which goes to modified versions that preserve MSAA. This is extremely brittle, and should not be expected to work with newer versions of unity.
The MSAA level can be configured from Preferences->Scene View MSAA.