feat(editing-support): add vim-visual-multi (#797)

* feat(editing-support): add vim-visual-multi

* Apply suggestions from code review

Co-authored-by: Micah Halter <micah@mehalter.com>

---------

Co-authored-by: Micah Halter <micah@mehalter.com>

lua/astrocommunity/editing-support/vim-visual-multi/README.md

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+# vim-visual-multi
+
+Multiple cursors plugin for vim/neovim.
+
+**Repository:** <https://github.com/mg979/vim-visual-multi>

lua/astrocommunity/editing-support/vim-visual-multi/init.lua

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+return {
+  "mg979/vim-visual-multi",
+  event = { "User AstroFile", "InsertEnter" },
+  dependencies = {
+    "astronvim/astrocore",
+    ---@param opts astrocoreopts
+    opts = function(_, opts)
+      if not opts.options then opts.options = {} end
+      if not opts.options.g then opts.options.g = {} end
+      opts.options.g.VM_silent_exit = 1
+      opts.options.g.VM_show_warnings = 0
+
+      if not opts.autocmds then opts.autocmds = {} end
+      opts.autocmds.visual_multi_exit = {
+        {
+          event = "User",
+          pattern = "visual_multi_exit",
+          desc = "Avoid spurious 'hit-enter-prompt' when exiting vim-visual-multi",
+          callback = function()
+            vim.o.cmdheight = 1
+            vim.schedule(function() vim.o.cmdheight = opts.options.opt.cmdheight end)
+          end,
+        },
+      }
+
+      if not opts.mappings then opts.mappings = require("astrocore").empty_map_table() end
+      local maps = assert(opts.mappings)
+      maps.n["<C-up>"] = { "<C-u>call vm#commands#add_cursor_up(0, v:count1)<cr>", desc = "Add cursor above" }
+      maps.n["<C-down>"] = { "<C-u>call vm#commands#add_cursor_down(0, v:count1)<cr>", desc = "Add cursor below" }
+    end,
+  },
+}