avro

Fix typos in C++ header files (#1033)

1. minumum -> minimum
2. valididated -> validated

Fix 1 typo in lang/c++/api/GenericDatum.hh:
1. appropraite ->  appropriate

Fix 3 typos in lang/c++/api/Decoder.hh:
1. fiedls -> fields
2. arbitray -> arbitrary
3. funtions -> functions

Fix 3 typos in lang/c++/api/DataFile.hh:
1. opportinity -> opportunity
2. entires -> entries
3. desrialize -> deserialize

Co-authored-by: Allen Reese <areese999@apple.com>