Deadlock in trace SDK shutdown

[jmacd]

Description

Updated to v1.13.x and noticed SDKs deadlocked in shutdown in some of our applications.
Some of our applications call TracerProvider.Tracer() in a gRPC interceptor to trace the RPC.
Our interceptors have been applied to the OTel trace SDK (by mistake, I'd say, but FWIW this worked before 1.13.x)
The interceptors are now deadlocking shutdown because Shutdown() holds the lock, preventing Tracer() from being called.

Environment

• OS: macOS
• Architecture: ARM
• Go Version: 1.19
• opentelemetry-go version: 1.13.0

Steps To Reproduce

Call Tracer() from an interceptor from an ExportSpans() call during Shutdown() and it will deadlock.

Shutdown() (takes lock) -> calls final ExportSpans() -> calls interceptor -> calls Tracer() (tries to get lock) == deadlocked

This appears to be introduced by #3551.

Expected behavior

The Shutdown should proceed. It looks safe to release the lock, meaning to replace the

	p.mu.Lock()
	defer p.mu.Unlock()
	p.isShutdown = true

with something equivalent to

	p.mu.Lock()
	if p.isShutdown {
	    p.mu.Unlock()
            return
        }
        p.isShutdown = true
	p.mu.Unlock()

[dmathieu]

It sounds like #3845 may be fixing this.