Bug tracking for annotation processor

[alzimmermsft]

Tracking list of bugs found while trying to performance test a library generated with annotation processor:

1. Variable name conflict when creating the HttpRequest.uri if there is a method parameter with the name url. String url is hardcoded as the variable name to use, ran across a case in Storage where the Swagger/TypeSpec defines a method parameter with name url which resulted in String url = url + ....
2. Handling of adding HTTP headers to HttpRequest will add them even if the value is null. In SwaggerMethodParser in azure-core null valued headers were excluded from being added. Worse, the null value will be stringified as "null", which makes any temporary fixes for cleaning more difficult as "null" could be a legitimate value.
3. When the network response status code doesn't match what's expected a very basic exception is thrown that loses all information provided by the error response. It is simply throw new RuntimeException("Unexpected response code: " + responseCode);, which isn't enough information to troubleshoot. Returning a proper exception needs to be done.
4. Storage Blob download has re-introduced a previous bug where Content-Type is being inspected before returning the download body, where Storage Blob allows providing metadata about the blob such as a JSON file being Content-Type: application/json. We want to explicitly ignore that for Storage Blob, and other APIs that may provide the same functionality, as we don't know how to handle the payload and should be returning a generic stream of bytes for the caller to manage converting to more specific data formats.
5. Methods with headers call HttpHeaderName.fromString each time when the header name isn't a constant. Annotation processing should be updated to collect all HttpHeaderName.fromString calls and convert those into statics on the service interface implementation. Possibly a common constants file shared across all generated interfaces as many services use the same headers in multiple service interfaces.
6. URI creation should use UriBuilder and remove the need for handling query parameters in a LinkedHashMap when collecting them to be handled.
7. Service interface implementations generate with JsonSerializer and XmlSerializer class level fields even when they aren't used. And a ClientLogger static variable as well. Those should be added at the end of code generation after we know they'll be used.

[alzimmermsft]

Points 1 and 2 were fixed in #45179

[alzimmermsft]

Point 4 is handled by #45188

[alzimmermsft]

Points 3 and 5 are handled by #45192