Remember selection mode

[wangp]

Is your feature request related to a problem? Please describe.
I like to initiate a text selection with a single/double/triple left click, then extend the selection (as required) with a single right click. This is much more comfortable than trying to select the text perfectly while holding down the left mouse button.

I managed to implement the behaviour in the Lua config as below, but perhaps it can be done more simply?

mouse_selection_mode = 'Cell'
config.mouse_bindings = {
  -- Single left-click: select cell
  {
    event = { Down = { streak = 1, button = 'Left' } },
    mods = 'NONE',
    action = wezterm.action_callback(function(win, pane)
      mouse_selection_mode = 'Cell'
      win:perform_action(act.SelectTextAtMouseCursor(mouse_selection_mode), pane)
    end)
  },
  -- Double left-click: select word
  {
    event = { Down = { streak = 2, button = 'Left' } },
    mods = 'NONE',
    action = wezterm.action_callback(function(win, pane)
      mouse_selection_mode = 'Word'
      win:perform_action(act.SelectTextAtMouseCursor(mouse_selection_mode), pane)
    end)
  },
  -- Triple left-click: select line
  {
    event = { Down = { streak = 3, button = 'Left' } },
    mods = 'NONE',
    action = wezterm.action_callback(function(win, pane)
      mouse_selection_mode = 'Line'
      win:perform_action(act.SelectTextAtMouseCursor(mouse_selection_mode), pane)
    end)
  },
  -- ALT+Left-click: select block
  {
    event = { Down = { streak = 1, button = 'Left' } },
    mods = 'ALT',
    action = wezterm.action_callback(function(win, pane)
      mouse_selection_mode = 'Block'
      win:perform_action(act.SelectTextAtMouseCursor(mouse_selection_mode), pane)
    end)
  },
  -- Single right-click: extend selection (current mode)
  {
    event = { Down = { streak = 1, button = 'Right' } },
    mods = 'NONE',
    action = wezterm.action_callback(function(win, pane)
      win:perform_action(act.ExtendSelectionToMouseCursor(mouse_selection_mode), pane)
    end)
  },
  {
    event = { Up = { streak = 1, button = 'Right' } },
    mods = 'NONE',
    action = act.CompleteSelection('ClipboardAndPrimarySelection')
  },
}

Describe the solution you'd like
ExtendSelectionToMouseCursor could take a mode (say, "Current" or "LastMode") that refers to the current selection mode. This was suggested previously in #182 and #282 (comment)