Summary:
Add the `--source-files-cfg` option to emit CFGs as .dot files just as if one
had run with `--debug` to begin with. The usual `--source-files-filter`
applies. For example:
```
$ cd examples
$ infer -- clang -c hello.c
$ infer --continue -- javac Hello.java
$ infer --continue -- make -C c_hello
$ infer explore --source-files --source-files-cfg --source-files-filter ".*\.c$"
hello.c
c_hello/example.c
CFGs written in /home/jul/infer.fb/examples/infer-out/captured/*/icfg.dot
```
Reviewed By: ezgicicek, mbouaziz
Differential Revision: D13973062
fbshipit-source-id: 3077e8b91