Android: replace deprecated PackageManager#getInstallerPackageName() with getInstallSourceInfo()

[aradhwan]

What

• Replace deprecated PackageManager#getInstallerPackageName(String) with
  PackageManager#getInstallSourceInfo(String).getInstallingPackageName() on API 30+,
  with a legacy fallback for <30.
• No Dart/API changes. No Gradle changes.

Why

• Fixes the deprecation warning reported in Android getInstallerPackageName Deprecated Warning #148 getInstallerPackageName(String) in PackageManager has been deprecated #151 InAppReviewPlugin.java uses or overrides a deprecated API. #155 Deprecated API warnings in InAppReviewPlugin.java (version 2.0.10) #165,
• Aligns with the modern Android API that supersedes getInstallerPackageName().

How I tested

• Ran flutter analyze – no issues.
• Built the example app on Android (SDK 34): the “uses or overrides a deprecated API” note referencing InAppReviewPlugin.java no longer appears.

Risk

• Low. Behavior preserved; guarded by runtime SDK check; falls back to the legacy call on older devices.

Closes #148 #151 #155 #165.

[britannio]

Thanks for the PR, I figured that a simpler solution is to avoid even checking the install source so I'm closing this in favour of
#167