Load native PHP extensions properly on Windows

[fredrikekelund]

Related issues

• Follow up to Build PHP binaries with Xdebug #3439
• Fixes RSM-2698

How AI was used in this PR

Claude drove the entire implementation based on a detailed spec from me.

Proposed Changes

#3439 changes the structure of the PHP package for Windows so that the extensions are no longer static but are distributed as separate DLL files. To account for this, we need to tell PHP where to find the extension files and to activate them. This PR does that.

This PR also activates Xdebug when the enableXdebug config is true.

Testing Instructions

1. Be on Windows
2. Download the Windows build from here
3. Extract it to C:\Users\USERNAME\.studio\php-bin\8.4 (replace the existing content)
4. npx cross-env STUDIO_RUNTIME=native-php npm start
5. Create a new site with PHP 8.4
6. Ensure that it starts as expected
7. Activate Xdebug in the site settings
8. Ensure that it works (you can add a phpinfo.php file in the site root and put a phpinfo() call in there for verification)

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[bcotrim]

I tested this and couldn't get the site to run in Windows using Studio app.

The failure I’m seeing appears to be unrelated to the extension-loading changes in this PR. It only happens when creating a site through Studio’s “Empty site” flow, using studio CLI directly works.
It appears to be related to running blueprints, are you able to replicate this issue?

[fredrikekelund]

To connect the dots: #3491 fixes the issue @bcotrim found with blueprints.

[wpmobilebot]

📊 Performance Test Results

Comparing 2cd6ea0 vs trunk

app-size

Metric	trunk	2cd6ea0	Diff	Change
App Size (Mac)	1354.95 MB	1354.95 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	2cd6ea0	Diff	Change
load	1471 ms	1498 ms	+27 ms	⚪ 0.0%

site-startup

Metric	trunk	2cd6ea0	Diff	Change
siteCreation	8616 ms	8568 ms	48 ms	⚪ 0.0%
siteStartup	4949 ms	4947 ms	2 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)