[API Proposal]: SummarizingChatReducer to be promoted as stable

[mdesalvo]

Background and motivation

Is it possible to have SummarizingChatReducer promoted as stable? So that the experimental marker (MEAI001) is removed and we are not forced to write this pragma for successfully building applications making use of it:

#pragma warning disable MEAI001

API Proposal

Just remove the [Experimental(MEAI001)] attribute on SummarizingChatReducer

Risks

The API is marked as experimental, removing the attribute makes it GA and promotes its adoption as an official IChatReducer implementation.