Bug 1728993 - Added JSON profile check that samples all look valid - r=florian

All profiles submitted to `JSONOutputCheck` are now checked for valid-looking samples, as in:
- Samples should point into the stackTable.
- stackTable entries should point to the caller in the same stackTable (or null for the root frame).
- stackTable entries should also point into the frameTable.
- frameTable entries should point into the stringTable for the "location".

Differential Revision: https://phabricator.services.mozilla.com/D124738