Opaque robj: add objectGetVal and remove ~80% of all robj->ptr refs

[SoftlyRaining]

I wanted to know if I could do this quickly by writing some scripts. It probably took twice as long as I thought, but only 3 hours so not terrible, and now I know. 🤷🏻‍♀️ Total number of references goes from ~400 to ~80, and all remaining references assign a value to robj->ptr. Those can be addressed in a separate PR, this one is big enough.

I know we want to make robj opaque so it's easier to refactor it or change its internal structure. I thought there was an issue for this but I can't find it offhand.

[codecov]

Codecov Report

Attention: Patch coverage is 83.67514% with 199 lines in your changes missing coverage. Please review.

Project coverage is 70.86%. Comparing base (78bcc0a) to head (634f526).
Report is 4 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/sentinel.c	0.00%	73 Missing ⚠️
src/module.c	1.92%	51 Missing ⚠️
src/debug.c	78.26%	20 Missing ⚠️
src/object.c	83.11%	13 Missing ⚠️
src/t_list.c	90.56%	5 Missing ⚠️
src/cluster_legacy.c	88.23%	4 Missing ⚠️
src/replication.c	89.74%	4 Missing ⚠️
src/t_stream.c	94.44%	4 Missing ⚠️
src/db.c	95.83%	3 Missing ⚠️
src/memory_prefetch.c	0.00%	3 Missing ⚠️
... and 13 more

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1658      +/-   ##
============================================
- Coverage     71.02%   70.86%   -0.17%     
============================================
  Files           121      121              
  Lines         65176    65206      +30     
============================================
- Hits          46290    46206      -84     
- Misses        18886    19000     +114     

Files with missing lines	Coverage Δ
src/bitops.c	93.77% <100.00%> (+0.30%)	⬆️
src/cluster_slot_stats.c	94.35% <100.00%> (ø)
src/commandlog.c	96.58% <100.00%> (ø)
src/config.c	78.40% <100.00%> (+0.01%)	⬆️
src/eval.c	57.06% <100.00%> (ø)
src/expire.c	96.59% <100.00%> (ø)
src/functions.c	94.50% <100.00%> (ø)
src/geo.c	93.58% <100.00%> (ø)
src/lazyfree.c	86.11% <100.00%> (ø)
src/multi.c	97.30% <100.00%> (ø)
... and 32 more

... and 5 files with indirect coverage changes

[zuiderkwast]

Awesome! Tbh, I'd prefer the complete change in one PR so we can get the benefit in memory usage. A separate commit within the same PR for the assignments and then a final commit to actually save memory in the object struct.

Feel free to write down you regexes so we can review those instead of alongside the actual diff. :D