PHP SAPI module

[adamziel]

What is this PR all about?

Introduces a PHP SAPI module that enables setting $_POST, $_SERVER, php://input and all the other PHP values from JavaScript.

What problem does it solve?

Before this PR, most superglobal values were set by prepending code snippets like $_SERVER['DOCUMENT_ROOT'] = ${JSON.stringify(documentRoot)}; every time some code was evaluated. Unfortunately, that technique couldn't populate everything, e.g. php://input remained empty.

How does it work?

PHP SAPI is used to integrate PHP with webservers and runtimes. A few SAPIs you might be familiar with are php-cgi, php-fpm, and php-cli. A SAPI consumes the request information from the runtime, passes it to PHP, triggers the code execution, and passes the response back to the runtime.

This PR introduces a WASM SAPI that accepts input information from JavaScript, sets up a PHP request, and passes a response back to JS. The most important changes are in the php_wasm.c file. The rest of the PR is adjusting the existing codebase to the new way of working with PHP.

Briefly speaking, the SAPI module exposes a few setters like wasm_set_query_string or wasm_add_SERVER_entry and a wasm_sapi_handle_request() function that triggers the request execution. The output information are written to /tmp/stdout, /tmp/stderr, and /tmp/headers.json by the C module and read by the PHP JavaScript class.

Because the request body and the query string are parsed by the same PHP internal functions as they would on a webserver, array syntax like settings[newsletter]=1 is handled correctly.

One surprising thing is the ability to set arbitrary $_FILES entries with wasm_add_uploaded_file. This is because JavaScript typically has access to any uploaded File objects and it would be wasteful to re-serialize them only so that PHP can parse them all over again. With wasm_add_uploaded_file you can first write the uploaded files to the filesystem and then simply let PHP know about their existence.

Solves #103

[adamziel]

PHP builds regenerated in 3a175a2