Use TraceIdentifier of HttpContext as a span in W3C when possible

[SergeyKanzhelev]

Motivation

TraceIdentifier is represented as a unique string. Implementation of TraceIdentifier should be aligned with migration to W3C. TraceIdentifier should match the span-ID in W3C distributed tracing context when possible.

CC: @seth-capistron, @vancem, @jacpull, @lmolkova, @glennc, @davidfowl

[muratg]

cc @shirhatti @davidfowl @Tratcher

[analogrelay]

Epic #8924

[analogrelay]

Waiting on an API on Activity to allow us to set the ID when we have one from the hosting server (IIS, etc.). Moved to 3.1 until we have this API.

[davidfowl]

@SergeyKanzhelev after looking at things I agree we should have a plan for this (hopefully as part of 3.0 even if execution happens in 3.1). Right now with activities and w3c, there's no good place to store the trace identifier so that it flows with the activity. (I'm not even sure if the format will align in all cases, but maybe we can make it)