Document cancellation behaviour

[yschimke]

Relating to #7016.

Document the issue with interrupts.

[swankjesse]

I think we should fix this rather than advising our users work around it?

Working around it is really hard for anyone canceling Futures that might transitively be performing OkHttp calls.

[yschimke]

@swankjesse +1Given the exception bubbles up from newStream to the caller through execute(), any pointers for how to address?

Exception in thread "Thread-11" java.io.InterruptedIOException: interrupted
	at okio.Timeout.throwIfReached(Timeout.kt:98)
	at okio.OutputStreamSink.write(JvmOkio.kt:54)
	at okio.AsyncTimeout$sink$1.write(AsyncTimeout.kt:99)
	at okio.RealBufferedSink.flush(RealBufferedSink.kt:267)
	at okhttp3.internal.http2.Http2Writer.flush(Http2Writer.kt:120)
	at okhttp3.internal.http2.Http2Connection.newStream(Http2Connection.kt:268)
	at okhttp3.internal.http2.Http2Connection.newStream(Http2Connection.kt:225)
	at okhttp3.internal.http2.Http2ExchangeCodec.writeRequestHeaders(Http2ExchangeCodec.kt:76)
	at okhttp3.internal.connection.Exchange.writeRequestHeaders(Exchange.kt:63)
	at okhttp3.internal.http.CallServerInterceptor.intercept(CallServerInterceptor.kt:41)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:109)```

a) Remove the stream + send rst_stream - and hope connection is healthy?
b) Assume connection is damaged and set noNewExchanges?
c) try to protect against this, avoid using the same user provided thread for an connection IO write?
d) try to minimise the window, make this effectively uninterruptible? Maybe requires support in Okio?
e) other?