not throw exceptions when class of annotation not found

[Liyw979]

When analysing single jar package, Sootup throws exceptions when some class of the annotation is missing.
In this PR:

1. Remove prefetch in getAnnotations since getDefaultValues is called in resolveDefaultsForAnnotationType.
2. Return empty map when the corresponding class is not found.
3. Allow users to do getAnnotations without the default values.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (647da14) 63.95% compared to head (21a0928) 63.68%.
Report is 122 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #726      +/-   ##
=============================================
- Coverage      63.95%   63.68%   -0.28%     
+ Complexity      3424     3342      -82     
=============================================
  Files            317      317              
  Lines          15391    15071     -320     
  Branches        2609     2542      -67     
=============================================
- Hits            9844     9598     -246     
+ Misses          4639     4588      -51     
+ Partials         908      885      -23     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[JonasKlauke]

Thanks for the small fix. Could you add a warning showing the missing annotation. So User will know that SootUp might need more data.

[JonasKlauke]

Thanks 👍