.Net: Graduate Filters feature

[markwallace-microsoft]

Checklist to be completed when graduating an experimental feature

• Verify the Filters feature is functionality complete (.Net: Filters use cases to be supported before making the feature non-experimental #5436)
• Are we keeping filter properties on the Kernel
• ​Verify API docs are complete and arrange to have them published
• Make appropriate updates to Learn docs​
• Make appropriate updates to Samples​​
• Verify there are no serious open Issues​​
• Verify there are sample implementations​ for the main use cases
• Update table in EXPERIMENTS.md
• Remove SKEXP​ flag from Filters code

[dmytrostruk]

Are we keeping filter properties on the Kernel

Based on comments, filter properties are still useful and adding new type of filters to Kernel type should not be complex: #6085 (comment).

[dmytrostruk]

Verify API docs are complete and arrange to have them published

• AutoFunctionInvocationContext Class
• IAutoFunctionInvocationFilter Interface
• FunctionInvocationContext Class
• IFunctionInvocationFilter Interface
• IPromptRenderFilter Interface
• PromptRenderContext Class

[dmytrostruk]

Update table in EXPERIMENTS.md
Remove SKEXP​ flag from Filters code

#7004