Make module docs customizable and update mod docs for crate reorg (#2418)

...lin/software/amazon/smithy/rustsdk/InlineAwsDependency.kt

...e/amazon/smithy/rustsdk/endpoints/AwsEndpointDecorator.kt

...smithy/rust/codegen/client/smithy/ClientCodegenContext.kt

...smithy/rust/codegen/client/smithy/ClientCodegenVisitor.kt

...zon/smithy/rust/codegen/client/smithy/ClientRustModule.kt

...gen/client/smithy/endpoint/EndpointConfigCustomization.kt

...rust/codegen/client/smithy/endpoint/EndpointsDecorator.kt

...amazon/smithy/rust/codegen/client/smithy/endpoint/Util.kt

...ent/smithy/endpoint/generators/EndpointParamsGenerator.kt

...t/smithy/endpoint/generators/EndpointResolverGenerator.kt

...degen/client/smithy/generators/NestedAccessorGenerator.kt

.../client/smithy/generators/client/FluentClientGenerator.kt

...lient/smithy/generators/protocol/ProtocolTestGenerator.kt

...amazon/smithy/rust/codegen/client/testutil/TestHelpers.kt

...re/amazon/smithy/rust/codegen/core/rustlang/RustModule.kt

...re/amazon/smithy/rust/codegen/core/rustlang/RustWriter.kt

.../amazon/smithy/rust/codegen/core/smithy/CodegenContext.kt

...mazon/smithy/rust/codegen/core/smithy/CodegenDelegator.kt

...ust/codegen/core/smithy/customize/CoreCodegenDecorator.kt

...software/amazon/smithy/rust/codegen/core/testutil/Rust.kt