Add activeDecodeTargets to AV1 DD JSON description

[JonathanLennox]

(This is only used for debug output.)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 44.24%. Comparing base (ec7d461) to head (93d73c5).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
...tensions/Av1DependencyDescriptorHeaderExtension.kt	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2322      +/-   ##
============================================
- Coverage     44.32%   44.24%   -0.09%     
- Complexity     2095     2097       +2     
============================================
  Files           351      351              
  Lines         19682    19739      +57     
  Branches       2660     2666       +6     
============================================
+ Hits           8724     8733       +9     
- Misses        10073    10120      +47     
- Partials        885      886       +1     

Files with missing lines	Coverage Δ
...tensions/Av1DependencyDescriptorHeaderExtension.kt	73.90% <0.00%> (-0.72%)	⬇️

... and 9 files with indirect coverage changes

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[bgrozev]

Not sure what the check does, but it should use the it reference