Feature: Group Header Checkbox

### What's the Problem?

In File Explorer, simply selecting the Group header when items are grouped selects all items in the group. This is not possible in Files.

### Solution/Idea

_I've come up with two ideas:_

**Long pressing the group header selects all items in group.**
_This would be approachable for both touch-screeners and mouse-clickers.

Considering accessibility,

**Adding a checkbox left of the Group header**
_Not everyone can long press.
_Not only would both touch-screeners and mouse-clickers be able to use it,
_It would also be user-friendly as it would be understandable that it is an option.

Consequently, this would allow the ability/add a feature to select multiple groups of items - _Which File Explorer does not have._

### Alternatives

As of now, there is no alternative way, I must resort to selection boxing items. Which is dreadful when selecting many items...

Perhaps instead of having checkboxes initially showing, when the Multiselect toggle is on, that a checkbox next to the Group header shall appear.

### Priorities

| Capability | Priority |
| :---------- | :------- |
| Ability to select all items within a Group | Must |
| Implement ideas: Checkbox, long-press, or both | Should |
| Ability to select multiple groups of items | Could |

### Files Version

Version: 2.3.0.0

### Windows Version

Windows 11 21H2 22000.778

### Comments

_No response_