Fixing rethrown exceptions to properly preserve stackframes.

[stebet]

Proposed Changes

This PR fixes those cases where exceptions were rethrown in a way that polluted the stackframes, making debugging/troubleshooting harder.

This is in line with the .NET guidelines on rethrowing exceptions:
https://docs.microsoft.com/en-us/visualstudio/code-quality/ca2200?view=vs-2019
https://docs.microsoft.com/en-us/archive/msdn-magazine/2015/november/essential-net-csharp-exception-handling#throwing-existing-exceptions-without-replacing-stack-information

Types of Changes

• Bug fix (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

[michaelklishin]

Backported to 6.x.