Use proper virtual file system for prompt files provider extension API

[pwang347]

[Copilot]

Pull request overview

This PR updates the chat prompt files provider API to use a proper virtual file system (vscode-chat-prompt) for inline prompt content, enabling consumers (including extensions) to read prompt content via the standard file APIs.

Changes:

• Expands the proposed prompt resource descriptor typing and updates ext host types accordingly.
• Introduces a vscode-chat-prompt file system provider backed by the in-memory prompt content store.
• Adds supporting plumbing: URI normalization for content lookup, an internal command to list extension prompt files, and markdown sanitization allowance for the new scheme.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/vscode-dts/vscode.proposed.chatPromptFiles.d.ts	Updates proposed API types so chat resources use a unified descriptor shape.
src/vs/workbench/contrib/chat/common/promptSyntax/chatPromptFilesContribution.ts	Adds an internal command to enumerate extension-contributed prompt files.
src/vs/workbench/contrib/chat/common/promptSyntax/chatPromptContentStore.ts	Normalizes vscode-chat-prompt URIs for stable content lookup across metadata variants.
src/vs/workbench/contrib/chat/browser/promptSyntax/chatPromptFileSystemProvider.ts	Adds an IFileSystemProvider for vscode-chat-prompt URIs to support workspace.fs reads.
src/vs/workbench/contrib/chat/browser/chat.contribution.ts	Ensures the new provider module is loaded/registered in the workbench.
src/vs/workbench/api/common/extHostTypes.ts	Aligns ext host wrapper types with the updated resource descriptor type.
src/vs/workbench/api/common/extHostChatAgents2.ts	Generates typed virtual URIs for inline prompt content and converts descriptors to IPC resources.
src/vs/base/browser/markdownRenderer.ts	Allows vscode-chat-prompt links through markdown sanitization.