Removing TrustService from Kernel.Core (to become extension) (#1895)

### Motivation and Context
The `TrustService`, along with related types like `TrustAwareString`
showcase a really interesting pattern, but we'd like to repackage them
into a `SemanticKernal.Extensions.Trust` package with a lot more
configurability, rather than baking these into the SK Core. With the
upcoming support for pre- and post- completion hooks in a Plan, we
believe we can build a better solution that leverages those hooks, but
is optional, configurable, and fully replaceable if our solution doesn't
meet your needs.

Other reasons:
- The `TrustAwareString` type is at odds with the transition we're
making to allow any objects (not just strings) in SK's context
variables, function args, and return types.
- Security issues have been raised by architects that indicate that this
pattern may give a false sense of security, as the strings in the
`TrustAwareString` objects can be manipulated by static casts, and are
therefore unreliable.
 
### Description
- Stripping out all `TrustService`, `TrustAwareString`, `IsSensitive`
and related references from the SK.Core and Abstractions packages.

**These will be added back in the form of a new
`SemanticKernel.Extensions.Trust` namespace with optional packages and
more features, including an auditable trust chain.

### Contribution Checklist
<!-- Before submitting this PR, please make sure: -->
- [X] The code builds clean without any errors or warnings
- [X] The PR follows SK Contribution Guidelines
(https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
- [X] The code follows the .NET coding conventions
(https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions)
verified with `dotnet format`
- [X] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

---------

Co-authored-by: Dmytro Struk <13853051+dmytrostruk@users.noreply.github.com>

dotnet/src/Extensions/Extensions.UnitTests/Planning/ActionPlanner/ActionPlannerTests.cs

@@ -9,7 +9,6 @@
 using Microsoft.SemanticKernel.Memory;
 using Microsoft.SemanticKernel.Orchestration;
 using Microsoft.SemanticKernel.Planning;
-using Microsoft.SemanticKernel.Security;
 using Microsoft.SemanticKernel.SemanticFunctions;
 using Microsoft.SemanticKernel.SkillDefinition;
 using Moq;
@@ -144,8 +143,7 @@ private Mock<IKernel> CreateMockKernelAndFunctionFlowWithTestString(string testP
         kernel.Setup(x => x.RegisterSemanticFunction(
             It.IsAny<string>(),
             It.IsAny<string>(),
-            It.IsAny<SemanticFunctionConfig>(),
-            It.IsAny<ITrustService?>()
+            It.IsAny<SemanticFunctionConfig>()
         )).Returns(mockFunctionFlowFunction.Object);
 
         return kernel;

dotnet/src/Extensions/Extensions.UnitTests/Planning/SequentialPlanner/SequentialPlanParserTests.cs

@@ -8,7 +8,6 @@
 using Microsoft.SemanticKernel.Orchestration;
 using Microsoft.SemanticKernel.Planning;
 using Microsoft.SemanticKernel.Planning.Sequential;
-using Microsoft.SemanticKernel.Security;
 using Microsoft.SemanticKernel.SemanticFunctions;
 using Microsoft.SemanticKernel.SkillDefinition;
 using Moq;
@@ -86,8 +85,7 @@ private void CreateKernelAndFunctionCreateMocks(List<(string name, string skillN
                 kernelMock.Setup(x => x.RegisterSemanticFunction(
                     It.IsAny<string>(),
                     It.IsAny<string>(),
-                    It.IsAny<SemanticFunctionConfig>(),
-                    It.IsAny<ITrustService?>()
+                    It.IsAny<SemanticFunctionConfig>()
                 )).Returns(mockFunction.Object);
             }
             else

dotnet/src/Extensions/Extensions.UnitTests/Planning/SequentialPlanner/SequentialPlannerTests.cs

@@ -10,7 +10,6 @@
 using Microsoft.SemanticKernel.Memory;
 using Microsoft.SemanticKernel.Orchestration;
 using Microsoft.SemanticKernel.Planning;
-using Microsoft.SemanticKernel.Security;
 using Microsoft.SemanticKernel.SemanticFunctions;
 using Microsoft.SemanticKernel.SkillDefinition;
 using Moq;
@@ -104,8 +103,7 @@ public async Task ItCanCreatePlanAsync(string goal)
         kernel.Setup(x => x.RegisterSemanticFunction(
             It.IsAny<string>(),
             It.IsAny<string>(),
-            It.IsAny<SemanticFunctionConfig>(),
-            It.IsAny<ITrustService?>()
+            It.IsAny<SemanticFunctionConfig>()
         )).Returns(mockFunctionFlowFunction.Object);
 
         var planner = new Microsoft.SemanticKernel.Planning.SequentialPlanner(kernel.Object);
@@ -192,8 +190,7 @@ public async Task InvalidXMLThrowsAsync()
         kernel.Setup(x => x.RegisterSemanticFunction(
             It.IsAny<string>(),
             It.IsAny<string>(),
-            It.IsAny<SemanticFunctionConfig>(),
-            It.IsAny<ITrustService?>()
+            It.IsAny<SemanticFunctionConfig>()
         )).Returns(mockFunctionFlowFunction.Object);
 
         var planner = new Microsoft.SemanticKernel.Planning.SequentialPlanner(kernel.Object);

dotnet/src/IntegrationTests/Planning/PlanTests.cs

@@ -146,7 +146,6 @@ public async Task CanExecutePanWithTreeStepsAsync()
     }
 
     [Theory]
-    [InlineData(null, "Write a poem or joke and send it in an e-mail to Kai.", null)]
     [InlineData("", "Write a poem or joke and send it in an e-mail to Kai.", "")]
     [InlineData("Hello World!", "Write a poem or joke and send it in an e-mail to Kai.", "some_email@email.com")]
     public async Task CanExecuteRunPlanSimpleManualStateAsync(string input, string goal, string email)
@@ -180,7 +179,6 @@ public async Task CanExecuteRunPlanSimpleManualStateAsync(string input, string g
     }
 
     [Theory]
-    [InlineData(null, "Write a poem or joke and send it in an e-mail to Kai.", null)]
     [InlineData("", "Write a poem or joke and send it in an e-mail to Kai.", "")]
     [InlineData("Hello World!", "Write a poem or joke and send it in an e-mail to Kai.", "some_email@email.com")]
     public async Task CanExecuteRunPlanSimpleManualStateNoVariableAsync(string input, string goal, string email)
@@ -214,14 +212,12 @@ public async Task CanExecuteRunPlanSimpleManualStateNoVariableAsync(string input
     }
 
     [Theory]
-    [InlineData(null, "Write a poem or joke and send it in an e-mail to Kai.", null)]
     [InlineData("", "Write a poem or joke and send it in an e-mail to Kai.", "")]
     [InlineData("Hello World!", "Write a poem or joke and send it in an e-mail to Kai.", "some_email@email.com")]
     public async Task CanExecuteRunPlanManualStateAsync(string input, string goal, string email)
     {
         // Arrange
         IKernel target = this.InitializeKernel();
-
         var emailSkill = target.ImportSkill(new EmailSkillFake());
 
         // Create the input mapping from parent (plan) plan state to child plan (sendEmailPlan) state.