Tools: Warn when pending model changes

[bricelam]

We should warn during the following commands when there are pending model changes that can be added to a new migration.

• Update-Database (dotnet ef database update) done in Warn on Migrate() when there are pending model changes #33732
• Script-Migration (dotnet ef migration script)
• Get-Migration (dotnet ef migration list)
• Get-DbContext -Context (dotnet ef dbcontext info)
  • Note, the output of this command could also be used programmatically (via --json) to test if there are any pending model changes (PR Add migrations has-pending-model-changes Command #31164)

[bricelam]

We should also consider adding sugar to the product (e.g. dbContext.Database.HasPendingModelChanges()) to do this since I've seen a lot of users asking how to over the years. (PR #31164)

[bricelam]

Some progress was made toward this in PR #14122

[bricelam]

We should also double check that the warning surfaces as part of the GenerateEFSQLScripts task and Publish dialog.