Some contribution points are not documented

[tamuratak]

The following contribution points are not documented at https://code.visualstudio.com/api/references/contribution-points:

• "chatAgents"
• "languageModelChatProviders"
• "languageModelTools"

Although "languageModelChatProviders" and "languageModelTools" are documented at https://code.visualstudio.com/api/extension-guides/ai/language-model-chat-provider, "chatAgents" is never mentioned anywhere.

See:

• https://github.com/microsoft/vscode/blob/cfb41fb5662b5c2a096e675720ed811409ea9ded/src/vs/workbench/contrib/chat/common/promptSyntax/chatPromptFilesContribution.ts