Add long-anim-frame & BrowserHitTransparent in "WebView2 browser flags"

[mikehoffms]

Rendered article section for review:

• WebView2 browser flags > Available WebView2 browser flags
  • /webview2/concepts/webview-features-flags.md
  • Internal preview: https://review.learn.microsoft.com/microsoft-edge/webview2/concepts/webview-features-flags?branch=pr-en-us-3416#available-webview2-browser-flags
  • External preview: https://github.com/MicrosoftDocs/edge-developer/blob/user/mikehoffms/flags-timing/microsoft-edge/webview2/concepts/webview-features-flags.md#available-webview2-browser-flags
  • Before/live: https://learn.microsoft.com/microsoft-edge/webview2/concepts/webview-features-flags#available-webview2-browser-flags
  • Added row long-animation-frame-timing.
  • Added row msWebView2BrowserHitTransparent.
  • Merged two rows for msWebView2CodeCache.
  • Added missing period on row msWebView2EnableDownloadContentInWebResourceResponseReceived.
  • Added instruction at top of table saying how all flags work.
    • Removed "if enabled" 14x & removed "if true" 3x, for consistency for Maintainers & users; established verb usage pattern.
  • Clarified that these flags are only for use during development, not in production.

AB#56766894

[learn-build-service-prod]

Learn Build status updates of commit 647c1b5:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/webview2/concepts/webview-features-flags.md	✅Succeeded	View

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[sivMSFT]

LGTM - PM

[mikehoffms]

LGTM - Writer/Editor