[clang-tidy] Restructure JSON profile structure to be parsable

[ilovepi]

The existing JSON output from --enable-profile uses the check names as
keys in the object. This limits the machine readability of the output,
as each key is unique, forcing consumers to split and parse the
substrings of the key itself to organize and extract information.

This change adapts the existing code to output more structured JSON. The
profile is now an array of 'checks', which each have a name that can be
queried and individual times for each of 'wall', 'user', 'sys', 'mem',
and 'instr'. We also make 'mem' and 'sys' non optional, since this makes
parsing uniform. Future patches can triage any inconsistency in the
numeric representation for 'mem' and 'sys', e.g. by using NAN, 0 or
another well defined sentinel value for JSON numbers.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[ilovepi]

So, when I thought this was only used for printing tidy JSON output, I assumed changing the implementation would only affect users of clang-tidy's profiling info. Since this seems to affect a plist output, I wonder if the old implementation should be kept around and renamed to something more fitting that isn't printJSON*?