global tracers and meters should be identified also by SchemeURL

[pellared]

From https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/api.md#get-a-tracer:

Tracers are identified by name, version, and schema_url fields.

From https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/api.md#get-a-meter:

Meters are identified by name, version, and schema_url fields.

We are missing SchemeURL in the key:

opentelemetry-go/internal/global/trace.go

Lines 104 to 107 in bf06b80

	type il struct {
	name string
	version string
	}

Originally posted by @pellared in #5366 (comment)