Fixed B3 Propagator

[owais]

Description

B3 propagator was returning None instead of invalid context after last
change. This resulted in many apps crashing when B3 failed to extract a
valid context from carrier. This PR patches it to not make apps crash
and return an invalid context when one cannot be extracted from the
carrier.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Added test case

Does This PR Require a Contrib Repo Change?

• Yes.
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[srikanthccv]

This should also fix the composite propagator issue. While you are at it, could you also fix another issue with B3 when there is a valid propagation header. context should be passed in this set_span_in_context call.

opentelemetry-python/propagator/opentelemetry-propagator-b3/src/opentelemetry/propagators/b3/__init__.py

Lines 114 to 125 in fba4e61

	return trace.set_span_in_context(
	trace.NonRecordingSpan(
	trace.SpanContext(
	# trace an span ids are encoded in hex, so must be converted
	trace_id=trace_id,
	span_id=span_id,
	is_remote=True,
	trace_flags=trace.TraceFlags(options),
	trace_state=trace.TraceState(),
	)
	)
	)

[owais]

Done. Also added tests to ensure the returned context is always derived from the provided one.