Add maven conguration to smithy-build.json

[srchase]

This CR updates SmithyBuildExtensions to use the following smithy-build.json format to allow setting Maven repositories and dependencies.

"maven": {
    "dependencies": ["com.foo.bar:custom-trait:0.0.1"],
    "repositories": [{
        "url": "https://url.to.maven.repo"
    }]
}

Existing smithy-build.json files will map mavenDependency and mavenRepositories arrays to the updated maven configuration. Configuration from the new maven key will be preferred over anything set in the deprecated mavenDependency and mavenRepositories keys.

Deprecation warnings with upgrade instructions are emitted to .smithy.lsp.log when the deprecated keys are encountered in smithy-build.json.

The MavenConfig and MavenRepository classes could eventually be moved to live with the existing SmithyBuildConfig model classes in aws-labs/smithy/smithy-build.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mtdowling]

Why is this an LSP feature and not part of smithy-build?

[srchase]

It definitely could be. My plan was to assure it meets the LSP's needs here before moving this functionality to smithy-build later on.

[mtdowling]

What API guarantees do we make in this repo? Can we yank this all out when it's moved to smithy-build?

[srchase]

On the IDE/Editor client side, there will just be a watcher that detects changes to smithy-build.json and notifies the server of updates to the file. No one should need to use SmithyBuildExtensions directly.