Add explicit | undefined for LanguageModelChatTool

[mjbvz]

Fixes #241285

This property can either be unset or set to undefined

[vs-code-engineering]

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[roblourens]

Why do you have to that explicitly? Isn't this essentially equivalent?

[mjbvz]

@roblourens Normally yes, but with exactOptionalPropertyTypes you have to specify if an optional property can be set to undefined instead of just being unset. This can be important as code sometimes treats something like foo({ abc: undefined }) as being different from foo({ }) where abc is omitted entirely. In our apis though we almost always treat them as being the same and this change makes that explicit

[roblourens]

Feel free to merge it if this is needed but why don't other optional properties in vscode.d.ts need this then?

[mjbvz]

We possibly should at some point but it's kind of a pain for limited real world benefit in most cases. This specific case is more important since you have two distinct types that were meant to be compatible (LanguageModelToolInformation and LanguageModelChatTool) but weren't because one used ? and the other | undefined