RID order guaranteed by avoiding iteration over a map

[j1elo]

Map iteration order is not guaranteed by Go, so it's an error to iterate over a map in places where maintaining the same ordering is important.

This change replaces the map of simulcastRid{} with an array of the same type. The simulcastRid{} type is extended to hold the rid-id which previously was used as the key in the map.

Accesses to the map are replaced with range loops to find the desired rid-id for each case.

Default code format applied.
Unit tests passed.

Fixes #2838

[j1elo]

A comment to the side: I'm thinking that what the original code did (and it's still done by the changed code) is to present the RIDs in the same order as the a=rid lines are found, not strictly speaking in the order of the a=simulcast attribute.

However, I'm not sure if that'd be an actual problem. I know that theoretically RIDs should be treated or given in the order found in a=simulcast... but in practice, does this matter? I've yet to see an instance where the a=rid lines come in a different order than the order of a=simulcast.

Practical SDP Offer example for readers who might be confused:

m=video 9 UDP/TLS/RTP/SAVPF ...
a=rid:layer0 send
a=rid:layer1 send
a=rid:layer2 send
a=simulcast:send layer0;layer1;layer2

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.92%. Comparing base (35b3ae1) to head (db89908).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2840   +/-   ##
=======================================
  Coverage   78.91%   78.92%           
=======================================
  Files          89       89           
  Lines        8314     8317    +3     
=======================================
+ Hits         6561     6564    +3     
  Misses       1276     1276           
  Partials      477      477           

Flag	Coverage Δ
go	80.51% <100.00%> (+<0.01%)	⬆️
wasm	64.88% <ø> (ø)

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[j1elo]

Great! thanks for the lint fixes, and for the work merging this.
A couple questions:

• Is the linter a default Go tool? I'd love to read more about it and see how to run it locally to avoid those naming mistakes in the future.
• Will this change be backported to v3? EDIT: I just saw it cherry-picked on v3 so that answers this question :)

[Sean-Der]

https://github.com/golangci/golangci-lint isn't a default Go tool, but is pretty popular! I don't know how I ended up on it.

I also added you to the org. Feel free to push tags and make branches w/e you need :)