Add Support for Power Fx as an Expression Type

[Copilot]

This PR adds support for Microsoft Power Fx as a new expression type in Elsa Workflows, providing an Excel-like formula language option for workflow expressions. This makes Elsa more accessible to citizen developers and business users who are familiar with Excel formulas but may not be comfortable with JavaScript or C# code.

Features

• Added a new module Elsa.Expressions.PowerFx that implements the Power Fx expression support
• Implemented PowerFxExpressionHandler to evaluate Power Fx expressions
• Created PowerFxEvaluator service to evaluate formulas using the Microsoft Power Fx engine
• Added PowerFxFeature for registering all required services
• Added helper extension method CreatePowerFx to the Expression class
• Added Monaco editor support with Excel syntax highlighting
• Created basic unit tests for the PowerFx evaluator

Example Usage

{
  "type": "PowerFx",
  "value": "If(Amount > 100 && Category = \"Premium\", true, false)"
}

Power Fx expressions can access workflow variables, inputs, and outputs, making them suitable for business rule conditions and calculations.

Fixes #6609.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• f.feedz.io
  • Triggering command: dotnet build src/modules/Elsa.Expressions.PowerFx/Elsa.Expressions.PowerFx.csproj (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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[sfmskywalker]

@copilot can you try and resolve the merge conflict please?

[Copilot]

@copilot can you try and resolve the merge conflict please?

I've resolved the merge conflict in Elsa.sln. The solution now includes both our PowerFx implementation and the Http.UnitTests project from the main branch. Commit 5905c07 contains the conflict resolution.