conform: disable autoformat on save for specified filetypes (#694)

Provide a method to disable autoformat on save lsp fallback for
specified filetypes. By default disable for C/C++ as an example,
because it does not have a well standardized coding style.

Based on conform recipe:
https://github.com/stevearc/conform.nvim/blob/master/doc/recipes.md

README.md

@@ -140,6 +140,8 @@ This will install the tree plugin and add the command `:Neotree` for you. For mo
 In the file: `lua/custom/plugins/filetree.lua`, add:
 
 ```lua
+-- File: lua/custom/plugins/filetree.lua
+
 return {
   "nvim-neo-tree/neo-tree.nvim",
   version = "*",

init.lua

@@ -603,10 +603,16 @@ require('lazy').setup({
     'stevearc/conform.nvim',
     opts = {
       notify_on_error = false,
-      format_on_save = {
+      format_on_save = function(bufnr)
+        -- Disable "format_on_save lsp_fallback" for languages that don't
+        -- have a well standardized coding style. You can add additional
+        -- languages here or re-enable it for the disabled ones.
+        local disable_filetypes = { c = true, cpp = true }
+        return {
           timeout_ms = 500,
-        lsp_fallback = true,
-      },
+          lsp_fallback = not disable_filetypes[vim.bo[bufnr].filetype],
+        }
+      end,
       formatters_by_ft = {
         lua = { 'stylua' },
         -- Conform can also run multiple formatters sequentially
@@ -711,6 +717,9 @@ require('lazy').setup({
               luasnip.jump(-1)
             end
           end, { 'i', 's' }),
+
+          -- For more advanced luasnip keymaps (e.g. selecting choice nodes, expansion) see:
+          --    https://github.com/L3MON4D3/LuaSnip?tab=readme-ov-file#keymaps
         },
         sources = {
           { name = 'nvim_lsp' },
@@ -787,8 +796,14 @@ require('lazy').setup({
       ensure_installed = { 'bash', 'c', 'html', 'lua', 'markdown', 'vim', 'vimdoc' },
       -- Autoinstall languages that are not installed
       auto_install = true,
-      highlight = { enable = true },
-      indent = { enable = true },
+      highlight = {
+        enable = true,
+        -- Some languages depend on vim's regex highlighting system (such as Ruby) for indent rules.
+        --  If you are experiencing weird indenting issues, add the language to
+        --  the list of additional_vim_regex_highlighting and disabled languages for indent.
+        additional_vim_regex_highlighting = { 'ruby' },
+      },
+      indent = { enable = true, disable = { 'ruby' } },
     },
     config = function(_, opts)
       -- [[ Configure Treesitter ]] See `:help nvim-treesitter`