.NET: Declarative Agents (#1301)

* AgentFactory abstractions and ChatClient implementation

* Add a getitng started sample

* Update to latest M.B.OM

* Add some additional samples

* Work in progress

* Merge latest from main

* Start to add support for using different kinds of connections

* Remove IsSupported

* Remove IsSupported

* Refactor code to create clients to support DI

* Add some unit tests

* Update based on the latest code review feedback

* Add support for OOB tools when using persistent agent sdk

* Fix sample naming

* Fix error based on latest MEAI

* Update M.B.OM package to latest

* Update to the latest M.B.OM release

* Remove some obsolete helper methods

* Update to the latest M.B.OM version

* Fix broken unit test

* Update MCP sample

* Bump to latest M.B.OM release

* Update to latest M.B.OM release

* Update to latest M.B.OM release

* Switch to using ExternalModel

* Update to latest M.B.OM

* Resolve merge conflicts

* All tests pass

* All tests pass

* Start to clean up the code

* Start to clean up the code

* More clean up

* More clean up

* More clean up

* Fix apiType checks

* Run dotnet format

* Fix typo

* Address code review feedback

* Add all properties for MCP tool

* Address code review feedback

* Address code review feedback

* Fix merge

* Undo warnings

* Undo test change

* More copilot feedback

* Make class sealed

* Address additional core review feedback

---------

Co-authored-by: Mark Wallace <markwallace@microsoft.com>

dotnet/Directory.Build.props

@@ -8,7 +8,7 @@
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     <LangVersion>13</LangVersion>
     <Nullable>enable</Nullable>
-    <NoWarn>$(NoWarn);NU5128</NoWarn>
+    <NoWarn>$(NoWarn);NU5128;NU1900;NU1603</NoWarn>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <ProjectsCoreTargetFrameworks>net9.0;net8.0</ProjectsCoreTargetFrameworks>
     <ProjectsDebugCoreTargetFrameworks>net9.0</ProjectsDebugCoreTargetFrameworks>