[PROF-11385] Enable GVL profiling by default on Ruby 3.2+

[ivoanjo]

What does this PR do?

This PR graduates the GVL profiling feature from preview to GA, and turns it on by default.

This means the old preview_gvl_enabled setting and its corresponding DD_PROFILING_PREVIEW_GVL_ENABLED environment variable are now deprecated.

Motivation:

Roll out this cool feature to customers ;)

Change log entry

Yes. Enable GVL profiling by default on Ruby 3.2+

Also, here's a snippet for the release highlights:

### GVL Profiling is now enabled by default on Ruby 3.2+

GVL profiling means the profiler gathers information from threads waiting to acquire the Ruby "Global VM Lock" (GVL).

This waiting can be a big a source of latency for Ruby applications: a thread "Waiting on the GVL" is a thread that's ready to make progress, but can't start because Ruby is busy doing something else.

For more details on why GVL profiling is relevant, check out [How the Ruby Global VM Lock impacts app performance](https://www.youtube.com/watch?v=MmKhsvvyiCw) and https://github.com/DataDog/dd-trace-rb/pull/3929.

Additional Notes:

N/A

How to test the change?

This change includes test coverage.

[datadog-datadog-prod-us1]

Datadog Report

Branch report: ivoanjo/prof-11385-gvl-profiling-ga
Commit report: 09eed91
Test service: dd-trace-rb

✅ 0 Failed, 20599 Passed, 1371 Skipped, 3m 16.63s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-19 10:45:25

Comparing candidate commit 09eed91 in PR branch ivoanjo/prof-11385-gvl-profiling-ga with baseline commit 18de083 in branch master.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 32 metrics, 2 unstable metrics.

scenario:tracing - Propagation - Trace Context

• 🟩 throughput [+3479.174op/s; +3578.863op/s] or [+10.161%; +10.452%]

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.70%. Comparing base (18de083) to head (09eed91).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4406      +/-   ##
==========================================
+ Coverage   97.69%   97.70%   +0.01%     
==========================================
  Files        1366     1366              
  Lines       83372    83396      +24     
  Branches     4230     4231       +1     
==========================================
+ Hits        81451    81483      +32     
+ Misses       1921     1913       -8     

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