feat(clipboard): add OSC 52 clipboard support

This is opt-in as not all terminal emulators support OSC 52, so it is up
to the user to enable it explicitly.

runtime/lua/vim/clipboard/osc52.lua

@@ -0,0 +1,38 @@
+local M = {}
+
+function M.copy(lines)
+  local s = table.concat(lines, '\n')
+  io.stdout:write(string.format('\x1b]52;;%s\x1b\\', vim.base64.encode(s)))
+end
+
+function M.paste()
+  local contents = nil
+  local id = vim.api.nvim_create_autocmd('TermResponse', {
+    callback = function(args)
+      local resp = args.data ---@type string
+      local encoded = resp:match('\x1b%]52;%w?;([A-Za-z0-9+/=]*)')
+      if encoded then
+        contents = vim.base64.decode(encoded)
+        return true
+      end
+    end,
+  })
+
+  io.stdout:write('\x1b]52;;?\x1b\\')
+
+  vim.wait(1000, function()
+    return contents ~= nil
+  end)
+
+  -- Delete the autocommand if it didn't already delete itself
+  pcall(vim.api.nvim_del_autocmd, id)
+
+  if contents then
+    return vim.split(contents, '\n')
+  end
+
+  vim.notify('Timed out waiting for a clipboard response from the terminal', vim.log.levels.WARN)
+  return 0
+end
+
+return M