Allow DecodedAudio ctor to accept a Buffer object

[borongc]

Add a DecodedAudio ctor to accept a Buffer object without extra copy.

b/275199195

[codecov]

Codecov Report

Merging #1486 (01c3fd1) into main (5e67ace) will increase coverage by 0.02%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

❗ Current head 01c3fd1 differs from pull request most recent head e5efc03. Consider uploading reports for the commit e5efc03 to get more accurate results

@@            Coverage Diff             @@
##             main    #1486      +/-   ##
==========================================
+ Coverage   56.37%   56.39%   +0.02%     
==========================================
  Files        1902     1902              
  Lines       94607    94612       +5     
==========================================
+ Hits        53330    53352      +22     
+ Misses      41277    41260      -17     

Files Changed	Coverage Δ
...d/shared/starboard/player/decoded_audio_internal.h	100.00% <ø> (ø)
.../shared/starboard/player/decoded_audio_internal.cc	86.93% <100.00%> (+0.33%)	⬆️

... and 5 files with indirect coverage changes