Add actionable error message for missing Azure package when Entra ID auth methods are used

[apoorvdeshmukh]

Description

Fixes #3962.

Issues

#3962

Testing

Added unit test

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[Copilot]

Pull request overview

This PR improves the error message when users attempt to use Active Directory (Entra ID) authentication methods without having the required Microsoft.Data.SqlClient.Extensions.Azure NuGet package installed. Previously, the error simply said "Cannot find an authentication provider for '{method}'", which was not actionable. Now it explicitly tells users to install the Azure extensions package.

Changes:

• Changed SQL.CannotFindAuthProvider to accept SqlAuthenticationMethod enum instead of string, and return a more helpful error message for Active Directory auth methods that includes the package name and NuGet URL.
• Added a new resource string SQL_CannotFindActiveDirectoryAuthProvider with actionable guidance.
• Added unit tests covering both Active Directory and non-Active Directory authentication methods.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlUtil.cs	Changed CannotFindAuthProvider parameter from string to SqlAuthenticationMethod and added switch to return AD-specific error message
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Connection/SqlConnectionInternal.cs	Updated call site to pass enum directly instead of .ToString()
src/Microsoft.Data.SqlClient/src/Resources/Strings.resx	Added new SQL_CannotFindActiveDirectoryAuthProvider resource string
src/Microsoft.Data.SqlClient/src/Resources/Strings.Designer.cs	Auto-generated property for the new resource string
src/Microsoft.Data.SqlClient/tests/UnitTests/Microsoft/Data/SqlClient/SqlUtilTests.cs	New unit tests verifying error messages for both AD and non-AD auth methods

Files not reviewed (1)

• src/Microsoft.Data.SqlClient/src/Resources/Strings.Designer.cs: Language not supported

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[benrr101]

Going forward, make sure that if you are reworking a PR to do the reworking in the same PR. If you close and resubmit a PR, all the comment history is wiped out, and it bypasses the requirement for a blocking review to be resolved before merging.