Separate vscode-dependent code from vscode-independent code

[hediet]

Currently, the project has exactly one runtime-dependency to VS Code:

vscode-prompt-tsx/src/base/index.ts

Lines 94 to 95 in b9b5bb4

	export function toVsCodeChatMessages(messages: ChatMessage[]) {
	const vscode = require('vscode');

(which currently breaks esbuild, see #40)

I recommend to use https://nodejs.org/api/packages.html#exports and to have a main entry point (import { render } from '@vscode/prompt-tsx';) and a vscode-specific part (import { toVsCodeChatMessages } from '@vscode/prompt-tsx/vscode';).

That way, you communicate that by default the main export has no runtime dependency on vscode (and thus, that the library is safe to use in traditional test-runners).