fix(android): check manifest declaration instead of grant state for FGS permission (fixes #731)

[ened]

Summary

requireForegroundServicePermission() in ForegroundServiceUtils.kt used PackageManager.checkPermission(), which reports the runtime grant state — not the manifest declaration. On Android 16+, foreground-service permissions can be revoked/denied at runtime even when declared, so the guard false-positived and threw:

expedited work (setExpedited) requires the 'android.permission.FOREGROUND_SERVICE_SHORT_SERVICE' permission in the merged manifest, but it is missing

…even though the merged manifest clearly declares it (see #731).

The guard now checks the merged manifest declaration instead: packageManager.getPackageInfo(packageName, PackageManager.GET_PERMISSIONS).requestedPermissions (the set of declared permissions). The loud IllegalStateException with the same fix hint is kept for genuinely missing declarations.

Behavior matrix after the fix:

Path	Manifest state	Result
Expedited / shortService	FOREGROUND_SERVICE_SHORT_SERVICE declared (plugin default)	passes — even if the runtime grant state is DENIED (Android 16+)
dataSync	workmanager.enableDataSyncForegroundService=true set (permission declared)	passes
dataSync	flag not set (permission absent)	still throws with the #725 fix hint

Verification

• ./gradlew :workmanager_android:testDebugUnitTest (via example app, JDK 17): 56 tests, 0 failures — including new tests covering both the declared case (shortService and dataSync) and the missing-declaration case, plus a null-requestedPermissions edge case.
• -Pworkmanager.enableDataSyncForegroundService=true build: confirmed the plugin swaps in the opt-in manifest and processDebugManifest output then contains FOREGROUND_SERVICE_DATA_SYNC.
• flutter build apk --debug (example app): builds clean.
• ktlint 1.7.1 (CI version) on the repo: clean. dart analyze: no issues.

Fixes #731