[Reader IA] Add dropdown menu analytics events

[RenanLukas]

Fixes #19906

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To Test:

• Install JP and sign-in;
• Open "Reader";
• Tap on the drop-down menu: you should see the following analytics event in the Logcat:

🔵 Tracked: reader_dropdown_menu_opened

• Tap each item in the drop-down menu (including a custom list item). You should see the following analytics events being tracked:

// When "Discover" is tapped
🔵 Tracked: reader_dropdown_menu_item_tapped, Properties: {"id":"discover"}
// When "Subscriptions" is tapped
🔵 Tracked: reader_dropdown_menu_item_tapped, Properties: {"id":"following"}
// When "Saved" is tapped
🔵 Tracked: reader_dropdown_menu_item_tapped, Properties: {"id":"saved"}
// When "Liked" is tapped
🔵 Tracked: reader_dropdown_menu_item_tapped, Properties: {"id":"liked"}
// When "Automattic" is tapped
🔵 Tracked: reader_dropdown_menu_item_tapped, Properties: {"id":"a8c"}
// When any item in a custom list is tapped (Menu -> Lists -> Tap any item)
🔵 Tracked: reader_dropdown_menu_item_tapped, Properties: {"id":"list"}

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Regression Notes

1. Potential unintended areas of impact
   None

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manual testing and unit tests.

3. What automated tests I added (or what prevented me from doing so)
   Updated ReaderTrackerTest.kt.

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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.

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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	pr19911-b581541
	Commit	b581541
	Direct Download	wordpress-prototype-build-pr19911-b581541.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	pr19911-b581541
	Commit	b581541
	Direct Download	jetpack-prototype-build-pr19911-b581541.apk

Note: Google Login is not supported on these builds.

[peril-wordpress-mobile]

	Warnings
⚠️	PR is not assigned to a milestone.

Generated by 🚫 dangerJS

[dangermattic]

	1 Warning
⚠️	PR is not assigned to a milestone.

Generated by 🚫 Danger

[daniloercoli]

LGTM!