Refactor use of HttpBindingIndex to simplify codegen

[jdisanti]

Several of the protocol code generators use the Smithy HttpBindingIndex class to determine which members belong to which parts of the HTTP request/response. The HttpBindingIndex only returns meaningful information if there are @http traits in the Smithy model, so it doesn't work for all of the protocols, but it would simplify the XML codegen if we could generalize this functionality over its uses in both AwsQuery and RestXml, and it may also simplify the JSON generators.

The idea is to create a generalized HttpBindingResolver that can use HttpBindingIndex if there are @http traits, or fall back to some default logic if there aren't.

[jdisanti]

Initial work is done. Just need to refactor AwsJson to use HttpBoundProtocolGenerator:
https://github.com/jdisanti/smithy-rs/blob/9e7a46e9b9d579144fd796ff2bcf962ac215f166/codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/protocols/AwsJson.kt#L186

[jdisanti]

This was fixed by #530.