Fix inconsistent background color of domain list in dark theme on landscape

[ovitrif]

Fixes #18269

This PR provides a very simple approach to fix the issue, basically adapting the existing implementation to use the proper Compose theme wrapper utility that we already had in the code.

To Test

Prerequisite

◐ Toggle the SiteCreationDomainPurchasingFeatureConfig flag

1. Go to Me → App Settings → Debug settings
2. Scroll to the Features in development section
3. Tap on the item corresponding to the flag
4. Tap RESTART THE APP button

● Treatment Variation

Verify the background color of domain list in site creation matches the screen bg in dark theme on landscape

1. Set the device in dark mode
2. Start the site creation flow
3. Select a design
4. Search for a domain
5. Turn the device in landscape mode
6. Verify that the background color is consistent

Preview

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 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.

UI Changes testing checklist:

• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• Talkback.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• Large and small screen sizes. (Tablet and smaller phones)
• Multi-tasking: Split screen and Pop-up view. (Android 10 or higher)

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr18320-5cb463b
	Commit	5cb463b
	Direct Download	wordpress-prototype-build-pr18320-5cb463b.apk

Note: Google Login is not supported on these builds.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr18320-5cb463b
	Commit	5cb463b
	Direct Download	jetpack-prototype-build-pr18320-5cb463b.apk

Note: Google Login is not supported on these builds.

[mkevins]

Great solution. Changing the color in compose is far simpler (compared to changing the activity), and the design still looks good, imo (actually, it is more consistent too). 👍

I tested this on a Pixel 3a, physical device.