Creating a new Span with a nil context causes a panic

[wildefires]

Description

Creating a new Span with a nil context causes a panic
Example https://go.dev/play/p/SXEK1EX_GzQ

Stack trace:

goroutine 1 [running]:
context.WithValue({0x0?, 0x0?}, {0x58aac0?, 0x6151e0?}, {0x5b9a20?, 0xc0002d4600?})
	/usr/local/go-faketime/src/context/context.go:525 +0x178
go.opentelemetry.io/otel/trace.ContextWithSpan(...)
	/tmp/gopath1305294289/pkg/mod/go.opentelemetry.io/otel/trace@v1.9.0/context.go:25
go.opentelemetry.io/otel/sdk/trace.(*tracer).Start(0xc00001e8c0?, {0x0?, 0x0?}, {0x5bf3e3?, 0x5?}, {0x0?, 0x60?, 0x726800?})
	/tmp/gopath1305294289/pkg/mod/go.opentelemetry.io/otel/sdk@v1.9.0/trace/tracer.go:58 +0x28c
main.main()
	/tmp/sandbox3842089424/prog.go:35 +0x264

IMO Otel should guard for this and if it's nil fill in a context.Background(). PR to do that: #3110

Environment

• OS: Linux
• Architecture: x64
• Go Version: 1.19
• opentelemetry-go version: 1.9.0 (based on panic stack trace)

Steps To Reproduce

1. Provide a nil context to Start() (see Go Playground link in description)

Expected behavior

Typical Otel behavior seems to either No-op or use reasonable defaults. While this panic isn't coming from the Otel lib, but rather an std lib, I'd still expect the sdk to - at worst - provide a NoOp span based on similar behavior in other parts