build: Add vulkan building script

[sapbotgit]

Overview

This PR adds build_vulkan.sh, a build script that automatically checks for all dependencies and compiles llama.cpp with the Vulkan backend enabled (-DGGML_VULKAN=ON).

Additional information

This script helps me (and hopefully others) build new llama.cpp versions faster by automating dependency checks and the compilation steps. I originally wrote a similar tool for personal use and have now adapted it for broader use.

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: Partly. Made by myself, but consulted with DeepSeek V3.2 for making this script maximally correct.

[jeffbolznv]

I don't think we should do this, we have build instructions for all platforms so I don't see why we would want a script that assumes a specific platform/compiler/generator. If cmake doesn't give good enough errors then we should try to improve the makefile.

[sapbotgit]

It's not so much about problems with help but about automation and faster recompilation for updates.