Capture/Replay: Optionally emit C sources. This adds an option that controls if we can write out simplified C replays. Once the work is finished we can remove the option and only allow emitting C instead of both C and CPP. Required emitting multi-line strings differently, as well as conditionalizing a few other language differences. Bug: angleproject:7713 Change-Id: I3303134316ed3fc1b4286bcd32961e8f7ecfbb06 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3953339 Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>