nvim: Move util to core.util module

Moved all utility functions from their own directory into
the core functionality direcotyr as a single file.

nvim/.config/nvim/lua/plugins/ide.lua

@@ -265,7 +265,7 @@ return {
 					}),
 				},
 			})
-			if require("util").is_available("which-key") then
+			if require("core.util").is_available("which-key") then
 				require("which-key").register({ ["<localleader>t"] = { name = "+test" } })
 			end
 		end,