Add "Select All" and "Invert" Shortcuts to Multiselect

[KyleTryon]

Is your feature request related to a problem? Please describe.
When using a multiselect component with a long list of options where you want to select many or all of the options, can be cumbersome as you must individually select each item.

Describe the solution you'd like
It can be helpful to be able to select all items in the list to quickly select and navigate from a long list. This also allows you to more easily deselect fewer options in the case you want to select most items but not all.

Add "Ctrl+a" for a Select All shortcut

Describe alternatives you've considered
Creating a new separate component with additional options

Additional context
An Inverse Selection addition may be good too, but could be addressed later.

Source: https://github.com/charmbracelet/huh/blob/main/field_multiselect.go
The Keymap

[caarlos0]

select all/none has landed on main #325

the inverse selection I'm not sure about... could you give some examples on how it would be useful?

thank you

[KyleTryon]

Awesome! 🎉

For inverse, it can be helpful when selecting many items from a long list.

For example, say you are selecting multiple directories in a list:

- /dir/1
- /dir/2
- /dir/3
- /dir/4
- /dir/5
- /dir/6
- /dir/7
- /dir/8

You want to select all, besides 1,2,3.

One way to achieve this would be to select 1,2,3 and then invert the selection.
The other way (which btw I think is acceptable with select all being available), is to select all, then un-select 1,2,3.