Changed vector_store_ids from required to optional

[NivedhaChellam]

Make vector_store_ids optional on FileSearchTool

Description:

Changes vector_store_ids from required to optional on OpenAI.FileSearchTool in the Foundry spec using @@withoutOmittedProperties + @@copyProperties override pattern.

This allows creating a file_search tool without pre-specifying vector store IDs upfront.

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API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
TypeSpec	Azure.AI.Projects

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