Renaming BroadcastActivity

[eddynaka]

Fixes #980, #979 .

Changes

Please provide a brief description of the changes here. Update the
CHANGELOG.md for non-trivial changes.

For significant contributions please make sure you have completed the following items:

• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1015 into master will increase coverage by 0.01%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1015      +/-   ##
==========================================
+ Coverage   77.01%   77.03%   +0.01%     
==========================================
  Files         220      220              
  Lines        6083     6083              
==========================================
+ Hits         4685     4686       +1     
+ Misses       1398     1397       -1     

Impacted Files	Coverage Δ
src/OpenTelemetry/Sdk.cs	94.04% <0.00%> (ø)
...elemetry/Trace/Internal/FanOutActivityProcessor.cs	92.50% <100.00%> (ø)
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	86.76% <0.00%> (+1.47%)	⬆️

[rajkumar-rangaraj]

Should we cast instead of creating a new. Earlier implementation of using IEnumerable was good. Is there a reason to change this to list?

[eddynaka]

Issue #980 points to a perf issue

[CodeBlanch]

My guess would be it was changed so that if the user changes it after the call, it won't impact us. But I like it because it will also save two allocations on every Activity (when doing the foreach in OnStart & OnEnd).

[reyang]

@rajkumar-rangaraj refer to this #735 (comment)