Add extension-src directive

[zeriyoshi]

Add extension-src directive to the php-ext section in composer.json.

This enables support for patterns where extension source code is not located in the project root, which is commonly seen in third-party extensions.

https://github.com/protocolbuffers/protobuf/tree/main/php/ext/google/protobuf

{
"name": "google/protobuf",
"type": "php-ext",
"description": "protocolbuffers php extension",
"php-ext": {
"extension-name": "protobuf",
"extension-src": "php/ext/google/protobuf"
}
}

[zeriyoshi]

I don't think this test failure was caused by the change, but I'm not familiar enough with Windows to know...
https://github.com/php/pie/actions/runs/11720819724/job/32646969527?pr=82#step:6:25

[asgrim]

@zeriyoshi thank you for this! However, I wish you had reported an issue first to discuss the requirement 😅 a lot of this code is currently being reworked at the moment to use a new pattern using the Composer Installer; it is absolutely feasible for us to accommodate this, but I'll need to take this on and rework this 😁

[zeriyoshi]

@asgrim
My apologies! I thought if you were going to make a suggestion, it would be better to have an example first (bad habit of mine).
I'm glad to know what's going on! Thank you very much!

[asgrim]

No worries at all :) it is still useful, and not wasted effort; I'll just need to rework it a bit shortly, so I'll hold off merging for now. I should be able to take a look next week. Thank you again 🙏

[asgrim]

Re-opened PR #115 to cover this - thanks @zeriyoshi !