The non-US backslash key still uses outdated, ambiguous GLFW terminology

In the fourth 26.3 snapshot GLFW was ditched for SDL3, however the international backslash key (KEY_102ND according to evdev) still appears to use the old GLFW terminology, which is misleading and has issues.

For one, whether “World 1” or “World 2” is used for this key is inconsistent from one operating system to another, and even on the same operating system depending on which display server is used (X11 uses World 1 whereas Wayland uses World 2): https://github.com/glfw/glfw/issues/2481

The name assigned to this key, in turn, is also overall unintuitive and non-indicative of its function.

This is easily reproduced by assigning a control to this key and checking the options.txt file, and by checking the en_us lang file for the presence of a World 1/World 2 translation string.

To fix this, one appropriately named key ID should be used for this specific key rather than two strangely named keys that differ from one computer to the next.