Accessibility: Add title to input url bar

[sejas]

• Closes https://github.com/WordPress/wordpress-playground/issues/615

Description

It adds an aria-label to the URL input bar for create-block/wasm-demo block.

Testing instructions

• In a terminal run:
  • yarn install
  • composer install
  • yarn wp-env start # to start the main server
• In a new terminal run:
  • cd source/wp-content/themes/wporg-wasm/src/wasm-demo
  • nvm use v14.21.3
  • yarn install
  • yarn start # to start the wasm demo block
• Go to /wp-admin
• Activate the theme Wasm if it's not active yet.
• Create a new page
• Embed the block wasm demo
• View the forntend page
• Inspect the settings input url bar with class wpplayground-url-bar__input
• Observe it has the title
• Run axe chrome extension
• Observe there is one less error.

Screenshot