This adds support for Chrome DevTools' "Emulate a focused page" feature to the VS Code JavaScript debugger.

Problem

When debugging web applications, the debugged page may lose focus to VS Code, causing focus-dependent behaviors (:focus styles, document.hasFocus(), focus event handlers) to not work as expected. Chrome DevTools has an "Emulate a focused page" option that solves this.

Solution

• Add new DAP custom requests canEmulate and setFocusEmulation to control focus emulation via CDP's Emulation domain
• Create a new "Debug Options" tree view (jsDebugOptions) that appears when debugging browser targets
• Allow users to toggle focus emulation with a checkbox that persists across debug sessions
• Only show the option for targets that support emulation (browser pages, not Node.js)

Implementation Details

• Uses Schema.getDomains to detect if Emulation domain is available
• Uses Emulation.setFocusEmulationEnabled CDP method
• Setting is persisted via workspace state

Verification Steps

• make sure you have js debug nightly installed

1. Create a simple HTML file with focus-dependent behavior:

   <input id="test" onfocus="console.log('focused')" onblur="console.log('blurred')" />
   <style>input:focus { outline: 3px solid blue; }</style>
   <script>setInterval(() => console.log('hasFocus:', document.hasFocus()), 2000);</script>

2. Start a browser debug session (e.g., "Debug: Open Link" or a Chrome launch config)
3. Click on the input field in the debugged page
4. Switch focus to VS Code — observe that document.hasFocus() returns false and the :focus style disappears
5. In the "Run and Debug" sidebar, find the new "Debug Options" panel
6. Check "Emulate a focused page"
7. Observe that document.hasFocus() now returns true and :focus styles remain even when VS Code has focus
8. Stop debugging and start again — verify the setting persists
9. Debug a Node.js app — verify the "Debug Options" panel is not shown (no emulation support)