Fix test tool hanging when restarting debugging session.

[normj]

Description of changes:
In the test tool if a user starts debugging their Lambda function, then stops debugging without letting the function finish it puts the test tool in hanging situation when the debug session is restarted. This happens because the first debug session never told the test tool that it was done processing the event so the test tool thinks the event is still active and executing. When the debug session is restarted and the GetNextInvocation is called it blocks waiting for the event to finish.

In the real Lambda environment the GetNextInvocation would never be called till the event is done processing. So when in the GetNextInvocation there should never be an active event still executing. For the test tool we will assume that if there is an active event with its status as executing that this is a debug restart scenario and resend the event to be debugged again.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[gcbeattyAWS]

just a general question. how does the lambda function/runtime know whether it should be calling either the GetNextInvocationDefaultFunction url vs calling the GetNextInvocation url? i assume if multiple lambdas are running at the same time they will use the url with their function name. in what case would the other url be called?

        app.MapGet("/2018-06-01/runtime/invocation/next", GetNextInvocationDefaultFunction);
        app.MapGet("/{functionName}/2018-06-01/runtime/invocation/next", GetNextInvocation);

[normj]

just a general question. how does the lambda function/runtime know whether it should be calling either the GetNextInvocationDefaultFunction url vs calling the GetNextInvocation url? i assume if multiple lambdas are running at the same time they will use the url with their function name. in what case would the other url be called?

        app.MapGet("/2018-06-01/runtime/invocation/next", GetNextInvocationDefaultFunction);
        app.MapGet("/{functionName}/2018-06-01/runtime/invocation/next", GetNextInvocation);

In the Lambda function if the AWS_LAMBDA_RUNTIME_API environment variable is set to localhost:<port> it will go to GetNextInvocationDefaultFunction. That is how we direct users in the current test tool which isn't designed for multiple functions. If you set AWS_LAMBDA_RUNTIME_API to localhost:<port>/<function-name> then it will go to GetNextInvocation. When we get to the Aspire integration we will set the environment this way.