Make AppSnippet parcelable

AppSnippet is used in Pia in 4 activities. Each time, it is expensive to
parse the app's logo and label from PackageManager and the APK file of
the app being installed. Thus, lets compute the AppSnippet once and pass
it as an intent extra to whichever activity needs it.

This also solves the bug where InstallSuccess showed an activity's name
in place of the app label since the temporary directory used to create
AppSnippet is already destroyed after app installation.

Bug: 290862169
Test: Manually install an APK and observe the app install / update
dialog

Change-Id: I2095b092e1a7b3186ff4cdc4c81effce51377b19