format-incremental - store modified files in bash array (#4717)
format-incremental - store modified files in bash array (#4717)

Split diff output at newlines and avoid storing files in a scalar that
needs to be split and may do wildcard expansion.  Simplify diff output
processing.  When formatting all files include only git-known sources.
quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq