Summary:
Emit the crucial parts of Pulse summaries as json to enable
post-processing by external tools. Stop somewhat arbitrarily at some
datatypes that are just emitted as "opaque" values.
For example:
```
$ infer debug --procedures --procedures-summary-json --select 0
[[["pulse",[["ContinueProgram",{"post":{"heap":[["v3",[[["Dereference"],["v4","_"]]]],["v7",[[["Dereference"],["v3","_"]]]]],"stack":[[["ProgramVar",{"plain":"return","mangled":null}],["v7","_"]]],"attrs":"_"},"pre":{"heap":[],"stack":[],"attrs":"_"},"skipped_calls":"_","path_condition":"_"}],["ContinueProgram",{"post":{"heap":[["v3",[[["Dereference"],["v4","_"]]]],["v8",[[["Dereference"],["v3","_"]]]]],"stack":[[["ProgramVar",{"plain":"return","mangled":null}],["v8","_"]]],"attrs":"_"},"pre":{"heap":[],"stack":[],"attrs":"_"},"skipped_calls":"_","path_condition":"_"}]]]]]
```
Reviewed By: ezgicicek
Differential Revision: D24503387
fbshipit-source-id: 9bd08e93b
Jules Villard