Consolidate fluent client builder implementations

[jdisanti]

Motivation and Context

The AWS fluent client implementation is currently separate from the generic Smithy fluent client implementation. The aim of this PR is to consolidate them so that changes made to one take effect in the other.

Testing

• Verified examples still compile and manually tested the S3 ListBuckets example

Checklist

• I have updated the CHANGELOG

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[jdisanti]

It looks like this PR makes passing around an individual operation's fluent builder more difficult. To illustrate how, here is a before/after snapshot from the Dynamo movies example:

Before:

fn create_table(
    client: &Client,
    table_name: &str,
) -> CreateTable {

After:

fn create_table(
    client: &Client,
    table_name: &str,
) -> CreateTable<DynConnector, AwsMiddleware, Standard> {

The PR currently has the clients arranged as follows:

crate
└── Client = crate::client::Client<DynConnector, AwsMiddleware, Standard>
crate::client
├── Client<C, M, R>
└── fluent_builders
    ├── SomeOperation<C, M, R>
    └── AnotherOperation<C, M, R>

I think we will need create a client::generic module and create a type alias for every operation's builder, as shown below:

crate
└── Client = crate::client::Client
crate::client
├── Client = Client<DynConnector, AwsMiddleware, Standard>
└── fluent_builders
    ├── SomeOperation = crate::client::generic::fluent_builders::SomeOperation<DynConnector, AwsMiddleware, Standard>
    └── AnotherOperation = crate::client::generic::fluent_builders::AnotherOperation<DynConnector, AwsMiddleware, Standard>
crate::client::generic
├── Client<C, M, R>
└── fluent_builders
    ├── SomeOperation<C, M, R>
    └── AnotherOperation<C, M, R>

@rcoh - What are your thoughts on this?

[rcoh]

can we conditionally generate default type parameters for the AWS case? Maybe we can have a defaultType map passed into the fluent builder core, something like:

data class DefaultTypes(connector: RuntimeType?, middleware: RuntimeType?, retry: RuntimeType?)

[rcoh]

this is huge and sorely needed. You can also undo my refactoring to create FluentClientCore when this lands.

[jdisanti]

can we conditionally generate default type parameters for the AWS case? Maybe we can have a defaultType map passed into the fluent builder core

That's a really good idea, I like it! Will give it a try.

[rcoh]

LGTM, one cleanup inline

[rcoh]

nit: probably clearer to have this be the retry module so that it's #{retry}::Standard which is much clearer than just Standard