Reader: Apply equal heights between navigation and filter buttons

[dvdchr]

Fixes #22533

Fixes a case where the buttons' height are different as the display size changes. To fix this, I applied frame(maxWidth: .infinity) to all the children of HStack and applied fixedSize to the stack view. This will cause the stack view to grow up to the tallest child, and all the remaining children will expand to fill the gap, matching the height of the tallest child.

Due to the contrast, it may appear that the buttons have a slight 1px height difference but that's probably an optical illusion! When measured through the visual debugger, they match:

To test

• Configure the phone or Simulator to use a larger display size
• Launch the Jetpack app
• Navigate to Reader and switch to Subscriptions
• 🔎 Verify that the Reader navigation buttons have equal heights

Regression Notes

1. Potential unintended areas of impact
   Should be none.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manually tested the changes.

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.

UI Changes testing checklist:

• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• 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)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[peril-wordpress-mobile]

	Warnings
⚠️	This PR is assigned to a milestone which is closing in less than 4 days Please, make sure to get it merged by then or assign it to a later expiring milestone

Generated by 🚫 dangerJS

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 24.2 ❄️. The due date for this milestone has already passed. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

Generated by 🚫 Danger

[wpmobilebot]

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

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr22544-06a721e
	Version	24.2
	Bundle ID	org.wordpress.alpha
	Commit	06a721e
	App Center Build	WPiOS - One-Offs #8682

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wpmobilebot]

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

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr22544-06a721e
	Version	24.2
	Bundle ID	com.jetpack.alpha
	Commit	06a721e
	App Center Build	jetpack-installable-builds #7710

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wargcm]

LGTM!