Add button to stop page load

[jruales]

• Adds "X" button to stop loading a website. This button shows instead of the reload button when the page is loading.
• Adds Escape key keybinding for the above action
  • Note: unlike other browser keybindings we've added, we don't prevent default, so that the page doesn't lose access to the Esc key
• When we stop loading a page, we don't show a fatal error. Instead, we ignore errors and just leave the page in a partially loaded state, as browsers normally do

Screen.Recording.2025-12-10.at.5.50.24.PM.mov

Added after the above video was recorded:

• Refresh button cooldown period to match Edge and Chrome behavior:
  • Add cooldown period of 500ms after clicking the reload button before it turns into the cancel button, to prevent accidental load cancellation when double-clicking
  • Reset the cooldown if the user moves the mouse out of the toolbar