Replace vim.opt with vim.o (#1495)

* Replace vim.opt with vim.o

Because it offers a nicer interface and info on hover.
For now leave vim.opt when using the table interface (until vim.o
with tables is implemented)

* Add type hint for vim.opt.rtp

* Add a comment about using vim.opt instead of vim.o

lua/kickstart/plugins/lint.lua

@@ -50,7 +50,7 @@ return {
           -- Only run the linter in buffers that you can modify in order to
           -- avoid superfluous noise, notably within the handy LSP pop-ups that
           -- describe the hovered symbol using Markdown.
-          if vim.opt_local.modifiable:get() then
+          if vim.bo.modifiable then
             lint.try_lint()
           end
         end,