More OpenTelemetry changes

[majocha]

• Add activity wrapping a test run to easily distinguish traces generated from testhost. Group by assembly + net framework.
• log point-in-time events as events with data instead of activities to declutter traces. (for example StackGuard.Guard)
• Enable trace provider in vsix when build in debug configuration: For example build VisualFSharpDebug in debug mode and start an instance with "Start WIthout Debugging" will produce traces viewable in Jeager.

Captured test run, some tests in parallel, a theory runs sequentially, Stackguard events with tags:

Traces from running VS instance:

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[majocha]

Slightly less allocations.

main:

Method	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
ParseAndCheckFileInProject	1.654 s	0.0225 s	0.0199 s	10000.0000	5000.0000	1000.0000	1.96 GB

this PR:

Method	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
ParseAndCheckFileInProject	1.625 s	0.0302 s	0.0297 s	9000.0000	4000.0000	1000.0000	1.91 GB

[psfinaki]

As with other OT changes, any Jaeger screenshots would be nice to have :)

[psfinaki]

Hi @majocha would you like to add something else here or is it getting ready to merge?

[majocha]

@psfinaki I think it's ok. Don't know how useful this will be in general, but it does reduce allocations a bit.

[psfinaki]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).