Fix: resolve mainTargetClassName correctly to handle activity aliases

[bunnyjaura]

Problem

When creating notifications in apps that use , the NotificationBuilder
was setting mainTargetClassName using only activityInfo.name. This caused a crash:

Attempt to invoke virtual method 'java.lang.String java.lang.Class.getName()'
on a null object reference

because the launcher alias did not have a direct activity class associated with it.

Solution

Updated updateMainTargetClassName() to:

1. Check activityInfo.targetActivity first.
2. Fall back to activityInfo.name if targetActivity is null.

This ensures that mainTargetClassName always points to a valid activity class,
even when the launcher entry is an alias.

Testing

• Verified with normal launcher activity (no alias).
• Verified with launcher alias.
• Notifications now open the correct main activity in all cases without crashing.

[bunnyjaura]

@rafaelsetragni