.NET: Update .NET package version 1.2.0

[lokitoth]

Description

• Minor version bump for next release
• Extract out the date version component so it is easier to update

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• [ ] Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

This PR updates .NET NuGet packaging metadata for the next release and also adjusts the handoff workflow’s message filtering behavior (with accompanying unit tests) in the Workflows layer.

Changes:

• Bump central NuGet VersionPrefix to 1.2.0, update GitTag, and extract the date component into DateSuffix.
• Refactor HandoffMessagesFilter logic to a simpler, ordering-dependent approach for filtering function-call/result content during handoffs.
• Add unit tests for HandoffMessagesFilter and factor out a reusable CreateHandoffResult helper.

Reviewed changes

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

File	Description
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/HandoffMessageFilterTests.cs	Adds unit tests intended to validate handoff/tool-call filtering behavior across modes.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/HandoffMessagesFilter.cs	Reworks filtering implementation for handoff/tool-call messages with stricter ordering assumptions.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/HandoffAgentExecutor.cs	Extracts creation of the “Transferred.” handoff tool result into a shared helper.
dotnet/nuget/nuget-package.props	Updates package versioning to 1.2.0 and introduces DateSuffix for easier preview version updates.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.