Vulkan: Enabling 16× MSAA freezes the editor

[Calinou]

Godot version: Git 3c1218a

OS/device including version: Fedora 31, NVIDIA 440.64, GeForce GTX 1080

Issue description: Setting MSAA to 16× in the Project Settings will cause the Godot editor window to freeze, while also freezing the OS for 10+ seconds. The editor window must be killed before the OS becomes smooth again.

This doesn't occur with lower MSAA values like 2×, 4× and 8×.

See #14727 (comment) for an explanation of why this likely happens only with 16× MSAA.

Steps to reproduce: Set Rendering > Quality > Screen Filters > Msaa to 16x. Note that the setting may be saved to the Project Settings if you're unlucky. If this happens, edit project.godot and remove the line quality/screen_filters/msaa=4 to make the project editable again.