[Bug]: Entra is still called Azure Active Directory

### Describe the bug

See https://github.com/search?q=repo%3AAzure%2Ftypespec-azure-pr%20%22Azure%20Active%20Directory%20OAuth2%20Flow%22&type=code

Per https://learn.microsoft.com/en-us/entra/fundamentals/new-name#naming-changes-and-exceptions, it needs to be renamed

### Reproduction

Here's a snippet from the top of a TypeSpec generated spec file:

```json
"securityDefinitions": {
"azure_auth": {
"type": "oauth2",
"description": "Azure Active Directory OAuth2 Flow.",
"flow": "implicit",
"authorizationUrl": "https://login.microsoftonline.com/common/oauth2/authorize",
"scopes": {
"user_impersonation": "impersonate your user account"
}
}
}
```

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/azure/typespec-azure/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that this issue is about the Azure libraries for typespec. For bug in the typespec language or core libraries file it in the [TypeSpec repo](https://github.com/Microsoft/TypeSpec/issues/new/choose)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.

Start with the repository search linked in the issue and reproduce the generated spec snippet to locate the source of the description. Update the outdated Azure Active Directory naming to Entra terminology, then verify the generated security definition no longer contains the old name.

Written by the indexing model from the issue text.