[Chapel Merge] Make the channel <~> operators into operator metho

Branch: refs/heads/main
Revision: 2ed0e01
Author: lydia-duncan
Log Message:

Merge pull request #18207 from lydia-duncan/channelOpChange

Make the channel <~> operators into operator methods
[reviewed by @bmcdonald3 - thanks!]

The last time I tried this, the calls were getting flagged as ambiguous.
Michael hypothesized that there might be something wrong with operator methods
and where clauses. Today, making this change seems to work - I think because I
fixed the general problem with where clauses getting ignored when one of the
argument actuals ends up being generic over in #18170.

Resolves #17538
Resolves Cray/chapel-private#2190

Passed a full paratest with futures

Modified Files:
M modules/standard/IO.chpl

Compare: https://github.com/chapel-lang/chapel/compare/2a51c90a6a06...2ed0e015b99e