[http-client-java] Java CodeGen should address the errors and warnings from TCGC

[lirenhe]

Clear and concise description of the problem

We need to empower our customers both internal and external to easily trouble shooting and fix spec issues that would block the CodeGen.

Today, TCGC could already do the check on the patterns and results from TypeSpec compiler and reports warning and errors for the unsupported case and invalid usage.

However, today our CodeGen didn't address those errors and warnings from TCGC in the implementation and in most cases would continue the codegen which would result in unexpected generated code & error. When that happens, the outcome would be difficult to trouble shooting.

Proposals:

• Java CodeGen need to display those warnings and errors in the command line output instead of ignoring them.
• Java CodeGen should properly address the errors and warnings from TCGC to provide a better user experience.

Checklist

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[weidongxu-microsoft]

TCGC diagnostics is reported via reportDiagnostics