Relabel or hide the Vulkan renderer option now that it is no longer maintained

[Reticulmz]

Type: Feature request / UX improvement

Background:
In a recent bug report regarding the Vulkan renderer (#37426), @bdach kindly clarified that the Vulkan backend is end-of-development in its current state and will not receive further fixes.

While I understand and respect that decision, the current presentation of this option in the settings UI may cause confusion for users who are unaware of its status, and could lead to duplicate bug reports being filed for issues that will not be addressed.

Proposal:
I would like to suggest the following UX improvements:

1. Relabel the option to reflect its actual status.
   The current label Vulkan (Experimental) implies that the backend is still under active development and may improve over time. A label such as Vulkan (Discontinued), Vulkan (Unmaintained), or Vulkan (No longer supported) would more accurately communicate its state to users.

2. Hide the option from the graphics settings UI by default.
   Since the backend is known to be broken in various scenarios and will not be fixed, exposing it as a selectable option in the settings menu invites users to try it, encounter problems, and file duplicate reports. Removing it from the default UI would prevent this.

3. Keep the backend accessible via an opt-in mechanism.
   For users who still want to use or test the Vulkan backend (whether out of curiosity, for testing purposes, or because it happens to work on their specific hardware), the option could be kept available through a command-line argument, environment variable, or a config file flag. This preserves the functionality for those who want it, while making it clear that using it is an explicit, unsupported choice.

Benefits:

• Reduces user confusion about the state of the Vulkan backend.
• Reduces the number of duplicate bug reports related to Vulkan issues.
• Respects the team's decision to stop maintaining Vulkan, while not removing it entirely.
• Provides a clearer signal to users that the default renderer is the supported path.

Related issue:

• Screen freezes when starting Ranked Play with Vulkan (Experimental) renderer on Pascal-generation NVIDIA GPUs #37426

cc @bdach

Thank you for considering this suggestion.

[peppy]

Experimental is fine. Experimental generally means don't use. If you have a problem, don' tuse.