Harmonize naming with glfw PR

[eliemichel]

This whole repo is meant to eventually be merged into GLFW imho, through this PR. When pushing there, I realized that calling the function glfwCreateWindowWGPUSurface instead of glfwGetWGPUSurface is more in sync with its Vulkan counterpart.

This repo will eventually undergo this renaming, but I want to make sure whenever I do this that the guide gets undated accordingly.