**Summary of the Pull Request**

This PR adds an X Macro for defining our ShortcutActions. This means that you can add the action in one place, and have the macro synthesize all sorts of boilerplate for you!

From the `AllShortcutActions.h` file:

> For a clearer explanation of how this file should be used, see:
> https://en.wikipedia.org/wiki/X_Macro
>
> Include this file to be able to quickly define some code in the exact same
> way for _every single shortcut action_. To use:
>
> 1. Include this file
> 2. Define the ON_ALL_ACTIONS macro with what you want each action to show up
>    as. Ex:
>
>    #define ON_ALL_ACTIONS(action) void action##Handler();
>
> 3. Then, use the ALL_SHORTCUT_ACTIONS macro to get the ON_ALL_ACTIONS marcro
>    repeated once for every ShortcutAction
>
> This is used in KeyMapping.idl, ShortcutAction.*, TerminalPage.*, etc. to
> reduce the number of places where we must copy-paste boiler-plate code for
> each action. This is _NOT_ something that should be used when any individual
> case should be customized.

**PR Checklist**
* [x] Scratches an itch
* [x] I work here
* [x] Tests passed
* [n/a] Requires documentation to be updated

**Detailed Description of the Pull Request / Additional comments**

Originally I had this blocked as a follow up to #9662. However, I've grown tired after a month of merging main into this branch, and I'm just shipping it separately. It will inevitably conflict with anyone who has actions in flight currently.

**Validation Steps Performed**
The code still builds exactly as before!