fix(neovim): use getnixpath util for nvim-dap and lsp, move polish

This moves polish.lua to `lua/`, creates a util.lua file to be loaded
before lazy.nvim so we can use the `getnixpath` util everywhere, and
replaces in polish.lua and lsp.lua the template strings for substitution
with a `getnixpath` equivalent

modules/home-manager/programs/neovim/lua/polish.lua

@@ -0,0 +1,16 @@
+-- This will run last in the setup process and is a good place to configure
+-- things like custom filetypes. This just pure lua so anything that doesn't
+-- fit in the normal config locations above can go here
+
+-- Set up custom filetypes
+vim.filetype.add {
+  extension = {
+    foo = "fooscript",
+  },
+  filename = {
+    ["Foofile"] = "fooscript",
+  },
+  pattern = {
+    ["~/%.config/foo/.*"] = "fooscript",
+  },
+}