feat(sdk-platform-java): Add CompositeTracer and CompositeTracerFactory. #543

Job	Run time
filter	1m 0s
build(8) for gapic-generator-java	11m 34s
build(8) for showcase	9m 43s
showcase-clirr	5m 10s
dependency_analyzer_unit_test	1m 13s
build (17)	14m 28s
showcase (17)	10m 23s
build(25) except self-service clients	12m 34s
build(21) except self-service clients	12m 46s
unmanaged_dependency_check	7m 35s
showcase (25)	10m 9s
build (11)	14m 58s
showcase (21)	10m 22s
gapic-generator-java-bom	2m 55s
showcase (11)	10m 11s
build(8) except for gapic-generator-java	4m 21s
	2h 19m 22s

Provide feedback