Rename global TraceProvider to TracerProvider

[MrAlias]

This naming was in error it should be TracerProvider.

opentelemetry-go/api/global/trace.go

Lines 30 to 39 in 1f2eba2

	// TraceProvider returns the registered global trace provider.
	// If none is registered then an instance of trace.NoopProvider is returned.
	//
	// Use the trace provider to create a named tracer. E.g.
	// tracer := global.TraceProvider().Tracer("example.com/foo")
	// or
	// tracer := global.Tracer("example.com/foo")
	func TraceProvider() trace.Provider {
	return internal.TraceProvider()
	}

[MrAlias]

This also needs to include SetTraceProvider -> SetTracerProvider in the same global package.