Suport filtering fields matching name predicate in avro schema generation.

RB=192500
R=mtagle,si-dev,jbetz,slim,luliu,gogenc
A=slim
Improve FileClassNameScanner to 1) require a specific extension; 2) exclude whose guessed class name contains dots.

RB=196098
BUGS=SI-886
R=gogenc,jbetz,si-dev
A=jbetz