feat: allow bindings for popup-smart-tab

[Sneethe]

A new zstyle; popup-smart-tab-bindings

This can be used to change what keybinds are "reversed" when tmux-popup shows above the cursor.

Examples

zstyle ':fzf-tab:*' fzf-bindings 'tab:toggle+down' 'btab:toggle+up'
zstyle ':fzf-tab:*' popup-smart-tab-bindings 'tab:toggle+up' 'btab:toggle+down'

Or

zstyle ':fzf-tab:*'fzf-bindings 'ctrl-g:top'
zstyle ':fzf-tab:*' popup-smart-tab-bindings 'ctrl-g:top+down'

Fixes:

• #383
• #390
• https://github.com/Aloxaf/fzf-tab/pull/326#issuecomment-1341147131