The root key in is incorrect when encoding shapes to XML

[epau]

Describe the bug

When we encode shapes to xml, we're currently producing the wrong root key.
There are two culprits.

1. The corresponding swift structs created have an Input suffix added to their name
2. We ignore the xmlName trait on the top level structure

Expected Behavior

Given the following smithy spec:

structure Foo {
    value: String
}

@xmlName("BarStruct")
structure Bar {
    value: String
}

We'd expect the encoded xml to look like the following:

<Foo><value></value></Foo>

<BarStruct><value></value></BarStruct>

Current Behavior

Given the same smithy spec as above, the current encoded xml looks like the following:

<FooInput><value></value></FooInput>

<BarInput><value></value></BarInput>

Reproduction Steps

N/A

Possible Solution

No response

Additional Information/Context

No response

AWS SWIFT SDK version used

0.5.0

Compiler and Version used

swift-driver version: 1.62.8 Apple Swift version 5.7 (swiftlang-5.7.0.127.4 clang-1400.0.29.50)

Operating System and version

12.6.1

[epau]

Closing in favor of awslabs/aws-sdk-swift#711