.NET: Log a warning when an unsupported declarative action is skipped

[tirdesh]

Motivation & Context

WorkflowActionVisitor routes 32 declarative action kinds to NotSupported, which records
the skip in two ways and neither reaches the caller. Debug.WriteLine is
System.Diagnostics.Debug, annotated [Conditional("DEBUG")], so the compiler removes the
call in Release. HasUnsupportedActions is declared on WorkflowActionVisitor, which is
internal sealed, and across the repository it is read in exactly one place, a unit test in
DeclarativeWorkflowTest.

The result is that a workflow containing SearchKnowledgeSources, InvokeFlowAction,
OAuthInput or any of the other 29 kinds builds, runs to completion and reports success
while never performing that step. In a Release build nothing is written anywhere.

The Python implementation already reports this. _declarative_builder.py in
_create_executor_for_action logs "Unknown action kind ... action will be skipped" and
returns None at the same point in the build, so the two languages currently disagree.

Description & Review Guide

• What are the major changes? NotSupported now logs a warning through the
  ILoggerFactory that DeclarativeWorkflowOptions already supplies to the visitor, naming
  the action type and id. The visitor creates one logger in its constructor. A regression
  test, UnsupportedActionLogsWarning, builds an AdaptiveDialog containing a
  SearchKnowledgeSources action and asserts a single warning carrying both values. Local
  checks: dotnet build -c Release (0 warnings, 0 errors),
  dotnet test -f net10.0 in Debug and in Release (878 passed, 0 failed), and
  dotnet format --verify-no-changes clean on both projects. Reverting only the source
  change and rerunning leaves 877 passing with UnsupportedActionLogsWarning failing.
• What is the impact of these changes? Control flow is unchanged and every action that
  was skipped before is still skipped. No public API is added, so the public API baselines
  and package validation are untouched. LoggerFactory defaults to
  NullLoggerFactory.Instance, so callers that configure no logging see no behavior change.
• What do you want reviewers to focus on? Debug.WriteLine is
  [Conditional("DEBUG")], so item.GetId() did not execute in Release before this change
  and now does. It is a plain property read that cannot throw for a DialogAction, and it
  renders as (null) for an action that carries no id.

If you would rather surface this as a WorkflowWarningEvent raised on first run instead of a
log, I am happy to change it.

Related Issue

Fixes #8040

No other open pull request for #8040 was found during the duplicate check.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change.

[Copilot]

🟢 Approval recommended

The focused implementation resolves the silent-skip issue with appropriate regression coverage and no identified defects.

Pull request overview

Adds visible warning logs when .NET declarative workflows skip unsupported actions, addressing issue #8040.

Changes:

• Creates a visitor-scoped logger and emits action type and ID warnings.
• Adds regression coverage verifying the warning.

File summaries

File	Description
WorkflowActionVisitor.cs	Logs unsupported skipped actions.
DeclarativeWorkflowTest.cs	Tests warning level and content.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced

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[tirdesh]

@microsoft-github-policy-service agree

[Vincent Biret (baywet)]

Thanks for the contribution!