Add typing information for contexts, token #812

Job	Run time
opentelemetry-api	39s
opentelemetry-exporter-opencensus	40s
opentelemetry-exporter-otlp-combined	43s
opentelemetry-exporter-otlp-proto-common	44s
opentelemetry-exporter-otlp-proto-grpc	41s
opentelemetry-exporter-otlp-proto-http	43s
opentelemetry-exporter-prometheus	36s
opentelemetry-exporter-zipkin-combined	39s
opentelemetry-exporter-zipkin-json	33s
opentelemetry-exporter-zipkin-proto-http	44s
opentelemetry-getting-started	48s
opentelemetry-opencensus-shim	41s
opentelemetry-opentracing-shim	40s
opentelemetry-propagator-b3	34s
opentelemetry-propagator-jaeger	33s
opentelemetry-proto-protobuf5	26s
opentelemetry-sdk	44s
opentelemetry-semantic-conventions	29s
opentelemetry-test-utils	35s
	12m 12s

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