Escape comma and backslash for list props

Comma is used as a separator for list props. To support comma on
StringList properties, elements are now escaped with backslashes.

Bug: 147402003
Test: fuzzing parser and formatter locally, sysprop_test, boot
cuttlefish

Change-Id: I69f1b5e7ba12746d982e9b05a62945a8746d9487
4 files changed