fix: ObjectKVStore::put on throwing __set

[PROFeNoM]

Motivation

In predis/predis, starting v2.1.2 w/ predis/predis#1049, it is no longer possible to use ObjectKVStore::put in versions 7.4 and below since Predis\Client::__set will be throwing an exception.

Currently, PredisIntegration is throwing an exception on versions 2.1.2+, using a PHP runtime that is strictly less than 7.4. Current estimates are reporting that ~5% of orgs using the predis integration are impacted.

Description

Fallback to spl_object_hash when it is not possible to use the weakmap nor __set.

This should allow to proceed with #3065.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.75%. Comparing base (c11372f) to head (dc021f3).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3066      +/-   ##
============================================
+ Coverage     72.97%   74.75%   +1.78%     
- Complexity     2790     2793       +3     
============================================
  Files           139      112      -27     
  Lines         15273    11047    -4226     
  Branches       1043        0    -1043     
============================================
- Hits          11145     8258    -2887     
+ Misses         3577     2789     -788     
+ Partials        551        0     -551     

Flag	Coverage Δ
appsec-extension	?
tracer-php	74.75% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/DDTrace/Util/ObjectKVStore.php	100.00% <100.00%> (ø)

... and 27 files with indirect coverage changes

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[bwoebi]

Let's not do that. This leaks memory and is never cleaned up.
(And throwing+catching an exception is also relatively expensive)
We just need another object to attach our data to, and I think $client->getConnection() is perfectly suited for that.