grpc-js: Fix interactions between proxy code and new URI parsing

[murgatroid99]

There were multiple issues here:

• We expect a proxy URL in the form http://host:port, but this does not actually fit with our naming scheme, so the URI parser parses it wrong. The solution is to revert to a previous version of getProxyInfo that parses the proxy address using the URL class.

• If the target had no scheme and was parsed weirdly into the GrpcUri structure, the resolver knew how to deal with that, but the proxy didn't, and it was making a bad request to the proxy. The solution is to stop using a default resolver, and instead modify the target at channel construction time so that it has a known scheme.

• The channel constructor was just overwriting the target after it got modified by the proxy.

• The proxy map result target didn't have an explicit scheme, even though it would definitely need to be interpreted as a DNS name. Added a scheme to fix that.

[ThWoywod]

It looks like like, that this fix do not really work.

I get the following error message:

[murgatroid99]

@ThWoywod Can you run your code with the environment variables GRPC_TRACE=all and GRPC_VERBOSITY=DEBUG, and share the log output?

[murgatroid99]

Never mind on the trace information. I believe I solved the problem in #1381. This time I managed to test it and I did successfully traverse a proxy and get a response from the server.

[ThWoywod]

Yeah thanks, with v 1.0.2 it works pretty well