CbmEvent: GetIndex() function re-implimentation and constant qualifiers for getters

• setting const qualifier to the GetIndex and the GetStsTrackIndex functions
• re-implimenting the GetIndex function to make it const qualified and reduce the number of access calls (from 3 to 1)

added Framework label

requested review from @f.uhlig

assigned to @v.friese

Dear @f.uhlig, @v.friese, @p.-a.loizeau,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

approved this merge request

added 2 commits

• 448e893b - 1 commit from branch computing:master
• 77e8d735 - CbmEvent:

Compare with previous version

@s.zharko,

since you touched the class, could you please have a look at core/data/test/_GTestCbmEvent.cxx to check if all the code is properly tested and add missing test cases.

resolved all threads

merged