Add header view to ActionSheetViewController

[wargcm]

Ref: #18402

Description

Allows for a header view to be added to the action sheet view controller. This will be used in a future PR for the blogging prompts header view.

Testing

To test:

• Sign into the app and navigate to the 'My Site' tab
• Tap on the floating create new action button
• Verify it functions as it previously did

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

You can test the changes in Jetpack from this Pull Request by:

• Clicking here or scanning the QR code below
• Then installing the build number pr18415-2ecd804 from App Center on your iPhone

The .ipa file can also be downloaded directly here.
If you need access to App Center, please ask a maintainer to add you.

[wpmobilebot]

You can test the changes in WordPress from this Pull Request by:

• Clicking here or scanning the QR code below
• Then installing the build number pr18415-2ecd804 from App Center on your iPhone

The .ipa file can also be downloaded directly here.
If you need access to App Center, please ask a maintainer to add you.

[ScoutHarris]

Hey Chris. I had one minor comment, but otherwise looks good!

[ScoutHarris]

I'm a bit confused about this name change. It looks like it's now a button title, but it's still the same header title. What it meant to clarify its use? I'm not sure it did. Maybe we can change it back?

[wargcm]

I can change it back. I just thought that it'd be confusing to have both the header view and something called a header title. Adding button was just to try and clarify it is the title for the buttons.