Initial SQL Capabilities SDK commit, with Capabilities API and comments

[nathannfan]

Description

Add Capabilities API to .NET SDK. Updated some descriptions to exclude enumeration values and simply reference the Capabilities API.

Swagger: Azure/azure-rest-api-specs#1015

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• I have read the contribution guidelines.
• The pull request does not introduce breaking changes.

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• Title of the pull request is clear and informative.
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Testing Guidelines

• Pull request includes test coverage for the included changes.

SDK Generation Guidelines

• If an SDK is being regenerated based on a new swagger spec, a link to the pull request containing these swagger spec changes has been included above.
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• The project.json and AssemblyInfo.cs files have been updated with the new version of the SDK.

[msftclas]

@nathannfan,
Thanks for your contribution as a Microsoft full-time employee or intern. You do not need to sign a CLA.
Thanks,
Microsoft Pull Request Bot

[cormacpayne]

@nathannfan please fill out the PR checklist provided, as well as provide a link to the corresponding rest-api-specs PR that this code was generated from

[nathannfan]

@cormacpayne Done. Haven't updated generate.cmd yet, as the REST hasn't been merged yet so I'm waiting for that.

[jaredmoo]

No test implemented?

[cormacpayne]

This PR should be merged at the same time as #2925 and #2927

[jaredmoo]

Combined into #2927 . I'm closing this since it will be reviewed and merged as part of #2927.