chore: update project configs to match cp.nvim

- Add .editorconfig
- Add .luarc.json for LSP support
- Rename .stylua.toml to stylua.toml
- Update .gitignore

.luarc.json

@@ -0,0 +1,8 @@
+{
+  "runtime.version": "Lua 5.1",
+  "runtime.path": ["lua/?.lua", "lua/?/init.lua"],
+  "diagnostics.globals": ["vim"],
+  "workspace.library": ["$VIMRUNTIME/lua", "${3rd}/luv/library"],
+  "workspace.checkThirdParty": false,
+  "completion.callSnippet": "Replace"
+}