Use flog symbols for drawing commit trees

[jbergstroem]

Flog symbols is a set of icons that a growing set of terminals (kitty, ghostty, wezterm wip) have decided to support via nerd-fonts. It would be visually pleasing to see lazygit use these as well!

Examples in use:

• https://github.com/SuperBo/fugit2.nvim
• https://github.com/isakbm/gitgraph.nvim
• https://github.com/rbong/vim-flog