@sentry/cloudflare/vite: Add a default export for the Vite plugin

Description

Add a default export to the @sentry/cloudflare/vite subpath, as an alias of sentryCloudflareVitePlugin, so the plugin can be imported under any name:

// vite.config.ts
import { cloudflare } from '@cloudflare/vite-plugin';
import sentry from '@sentry/cloudflare/vite';
import { defineConfig } from 'vite';

export default defineConfig({
  plugins: [cloudflare(), sentry()],
});

sentryCloudflareVitePlugin stays the documented name, so this is additive and breaks nothing.

// packages/cloudflare/src/vite/index.ts
export default sentryCloudflareVitePlugin;

Why

• Most Vite plugins default-export, for example @vitejs/plugin-react, vinext and nitro/vite. A default export matches what users expect at that place in the config.
• The call site reads better with a short local name: plugins: [cloudflare(), sentry()].
• There is precedent in this repo: @sentry/astro default-exports its integration, and @sentry/nuxt its module.

Notes

• The ./vite subpath currently also declares a require condition. In CJS, a default export is reached as require('@sentry/cloudflare/vite').default. The comment at the top of src/vite/index.ts says the CJS entry cannot resolve anyway (@sentry/server-utils/orchestrion/vite has no require condition), and Vite configs are ESM in practice, so this is acceptable.
• Sentry's other Vite plugins (@sentry/vite-plugin, SvelteKit, SolidStart) use named exports only, so this makes the Cloudflare one the exception. The named export stays, and docs keep using it.
• The subpath exports more than the plugin (the options type today), so the JSDoc on the default export should state that it is an alias of sentryCloudflareVitePlugin.

Scope

• export default sentryCloudflareVitePlugin; in packages/cloudflare/src/vite/index.ts, with JSDoc.
• A test asserting the default export is the same function as the named one.
• Optionally a docs snippet showing the short import.