`./gradlew :aws:sdk:assemble` fails on Windows for several reasons

[Velfi]

The crate-hasher crate isn't Windows-compatible. Even after adding a #[cfg(windows)] to fix that, smithyBuild will fail with:

Execution failed for task ':aws:sdk:smithyBuild'.
> Failed to calculate the value of task ':aws:sdk:smithyBuild' property 'outputDir'.
   > Failed to query the value of extension 'smithy' property 'outputDirectory'.
      > Error parsing JSON: Expected valid escape sequence ([33, 46])

This makes it impossible to develop codegen-related code on Windows.