Gate New Stats behind remote feature flag

[adalpari]

Description

The New Stats experience was previously gated by a local experimental
feature flag (ExperimentalFeatures.Feature.NEW_STATS), toggled both from the
experimental-features settings screen and from in-app "Try new stats" /
"Disable new stats" controls.

This PR replaces that local flag with a new remote feature flag,
android_new_stats, so the rollout can be controlled server-side. The remote
flag is the single source of truth for routing (which Stats screen opens by
default) and defaults to false when the remote value is unavailable (offline /
not yet fetched).

The in-app switch controls are kept so users can move between the classic
and new experiences, with one rule tied to the remote flag: when
android_new_stats is on, the new experience is the rollout default and the
user is locked into it (no "Disable new stats" action). When the flag is
off, both directions are available. The controls are now plain navigation —
they no longer persist any local flag, so the remote flag remains the routing
source of truth.

Changes

• New remote flag: added NewStatsFeatureConfig (@Feature("android_new_stats", false))
  and the NEW_STATS buildConfigField. The @Feature annotation auto-registers
  the default in the KSP-generated RemoteFeatureConfigDefaults.
• Gating read swapped: ListItemActionHandler now decides new vs. classic
  Stats via newStatsFeatureConfig.isEnabled() (test updated accordingly).
• Local flag removed: dropped the NEW_STATS entry from ExperimentalFeatures
  (it disappears from the experimental-features settings screen automatically).
• "Try new stats" kept on the classic screen: the toolbar menu
  (res/menu/stats_toolbar_menu.xml) and the "new Stats experience" suggestion
  dialog in StatsFragment remain. Selecting them now simply launches
  NewStatsActivity (no local flag write).
• "Disable new stats" kept on the new screen, gated on the remote flag: the
  overflow action in NewStatsActivity is shown only when
  newStatsFeatureConfig.isEnabled() is false. When the remote flag is true
  the action is hidden, so users on the rollout cannot switch back. Selecting it
  launches the classic StatsActivity (no local flag write).
• Retained the supporting suggestion prefs (AppPrefs/AppPrefsWrapper), base
  English strings, and the STATS_NEW_STATS_ENABLED/STATS_NEW_STATS_DISABLED
  analytics events used by these controls.

Testing instructions

Remote flag off (default):

1. Build & install the Jetpack debug app on a WordPress.com or Jetpack-connected site.
2. Open My Site → Stats.

• Verify the classic Stats screen opens.
• Verify the "Try new stats" toolbar menu item is present, and the "A new Stats experience" suggestion dialog appears on first eligible launch.
• Tap "Try new stats" (or "Try it out") → verify the new Stats screen opens.
• In the new Stats screen, verify the overflow "Disable new stats" action is present and returns you to the classic Stats screen.

3. Open Me → App Settings → Experimental Features (debug).

• Verify "New Stats" is no longer listed.

Remote flag on:

1. Force-enable the flag locally by setting NEW_STATS to "true" in WordPress/build.gradle (or enable android_new_stats via remote config), then rebuild.
2. Open My Site → Stats.

• Verify the new Stats screen opens directly.
• Verify the overflow "Disable new stats" action is not shown (user is locked into New Stats).

[dangermattic]

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[wpmobilebot]

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

	App Name	Jetpack Android
	Build Type	Debug
	Version	pr22996-555b307
	Build Number	1496
	Application ID	com.jetpack.android.prealpha
	Commit	555b307
	Installation URL	5uaeniluh2898

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[wpmobilebot]

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

	App Name	WordPress Android
	Build Type	Debug
	Version	pr22996-555b307
	Build Number	1496
	Application ID	org.wordpress.android.prealpha
	Commit	555b307
	Installation URL	5pvoiqn87f838

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

[wpmobilebot]

🤖 Build Failure Analysis

This build has failures. Claude has analyzed them - check the build annotations for details.

[codecov]

Codecov Report

❌ Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.46%. Comparing base (0225fe2) to head (555b307).
⚠️ Report is 1 commits behind head on trunk.

Files with missing lines	Patch %	Lines
.../wordpress/android/ui/newstats/NewStatsActivity.kt	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk   #22996      +/-   ##
==========================================
- Coverage   37.46%   37.46%   -0.01%     
==========================================
  Files        2325     2326       +1     
  Lines      125221   125224       +3     
  Branches    17160    17162       +2     
==========================================
  Hits        46913    46913              
- Misses      74502    74505       +3     
  Partials     3806     3806              

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