Better code generation checking for Pull Request pipelines

[alzimmermsft]

Description

This PR resolves an issue where Pull Request pipelines lacked granularity when running code generation validation. The /sdk/<service> folder would be scanned rather than the more granular /sdk/<service>/<library> directory. This resulted in inadvertent validation that could fail a run that didn't make changes to that directory and would generally just validate more than needed.

Now, the library folders are scanned instead which scopes validation to just the libraries that were modified in the PR.

There was also minor house cleaning on the PowerShell scripts to use better names.

There is a temporary change in Call Automation to validate none of the other Communication libraries are validated.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.