Endpoint test generator produces code with non-deterministic order

[jdisanti]

In a PR unrelated to endpoints, I noticed the PR Bot's diff showed a reordering of all the endpoint test param insertions. For example:

                 .property(
                     "authSchemes",
                     vec![aws_smithy_types::Document::from({
                         let mut out =
                             std::collections::HashMap::<String, aws_smithy_types::Document>::new();
-                        out.insert("name".to_string(), "sigv4".to_string().into());
                         out.insert("disableDoubleEncoding".to_string(), true.into());
+                        out.insert("name".to_string(), "sigv4".to_string().into());
                         out.insert("signingName".to_string(), "s3".to_string().into());
                         out.insert("signingRegion".to_string(), "us-west-2".to_string().into());
                         out
                     })]
                 )

All the code in this highlighted area needs to use deterministic ordering when iterating over Map types:
https://github.com/awslabs/smithy-rs/blob/a15ce735b9209e42d2e4ea2025ce92cca9d91e0b/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/generators/EndpointTestGenerator.kt#L100-L152

[jdisanti]

Saw it on another PR unrelated to endpoints:

                 .property(
                     "authSchemes",
                     vec![aws_smithy_types::Document::from({
                         let mut out =
                             std::collections::HashMap::<String, aws_smithy_types::Document>::new();
-                        out.insert("signingName".to_string(), "s3-outposts".to_string().into());
                         out.insert("signingRegion".to_string(), "us-east-2".to_string().into());
-                        out.insert("disableDoubleEncoding".to_string(), true.into());
                         out.insert("name".to_string(), "sigv4".to_string().into());
+                        out.insert("signingName".to_string(), "s3-outposts".to_string().into());
+                        out.insert("disableDoubleEncoding".to_string(), true.into());
                         out
                     })]
                 )