Fix serializing all stack trace frames

[felixbarny]

What does this PR do?

closes #1570

Checklist

• This is an enhancement of existing features, or a new feature in existing plugins
  • I have updated CHANGELOG.asciidoc
  • I have added tests that prove my fix is effective or that my feature works
  • Added an API method or config option? Document in which version this will be introduced
  • I have made corresponding changes to the documentation
• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix
• This is a new plugin
  • I have updated CHANGELOG.asciidoc
  • My code follows the style guidelines of this project
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • New and existing unit tests pass locally with my changes
  • I have updated supported-technologies.asciidoc
  • Added an API method or config option? Document in which version this will be introduced
  • Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• This is something else
  • I have updated CHANGELOG.asciidoc

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Build stats

• Build Cause: Pull request #1571 updated

• Start Time: 2020-12-15T15:49:20.581+0000

• Duration: 46 min 7 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1633
Skipped	12
Total	1645

[codecov-io]

Codecov Report

Merging #1571 (2e266ea) into master (81688c7) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1571      +/-   ##
============================================
+ Coverage     58.98%   58.99%   +0.01%     
  Complexity       92       92              
============================================
  Files           391      391              
  Lines         17615    17617       +2     
  Branches       2436     2437       +1     
============================================
+ Hits          10390    10394       +4     
  Misses         6508     6508              
+ Partials        717      715       -2     

Impacted Files	Coverage Δ	Complexity Δ
.../apm/agent/report/serialize/DslJsonSerializer.java	89.19% <100.00%> (+0.14%)	0.00 <0.00> (ø)
...ic/apm/agent/profiler/collections/LongHashSet.java	16.66% <0.00%> (-1.20%)	0.00% <0.00%> (ø%)
.../bci/bytebuddy/SoftlyReferencingTypePoolCache.java	93.75% <0.00%> (+12.50%)	0.00% <0.00%> (ø%)

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