Re-examine usage of `mavenLocal`

[ianbotsf]

We use mavenLocal in our Gradle build scripts fairly liberally throughout our project. Gradle's documentation discourages the use of mavenLocal and recommends alternatives such as composite builds.

Examine each of our usages of mavenLocal and determine whether it could be:

• Removed
• Replaced by a composite build
• Scoped tighter with content filtering

Applies to aws-sdk-kotlin, smithy-kotlin, aws-crt-kotlin, and aws-kotlin-repo-tools.