vim-anywhere lets you invoke gVim to edit any text on your Linux or macOS machine. The vim-anywhere is available from https://github.com/cknadler/vim-anywhere. Once installed, place your cursor in a text field, and press Ctrl + Cmd + v on macOS or Ctrl + Alt + v on Linux. Depending on your platform, vim-anywhere will open either MacVim or gVim, as shown in the following screenshot:

Save the buffer, exit MacVim or gVim, and vim-anywhere will insert the buffer contents into the original text field.