[PHP] Inline rotatePHPRuntime() into the PHP class

[adamziel]

Motivation for the change, related issues

Moves the rotatePHPRuntime() logic inside the PHP class and properly await them to prevent async rotation failures:

{
  type: 'request.error',
  error: Error: PHP.run() failed with exit code 255.
      at runExecutionFunction.then.dispatchEvent.type (/Users/cloudnik/www/Automattic/core/plugins/wordpress-playground/packages/php-wasm/universal/src/lib/php.ts:1052:14),
  source: 'php-wasm'
}
Trace: hotSwapPHPRuntime called on a disposed PHP instance
    at PHP.hotSwapPHPRuntime (/Users/cloudnik/www/Automattic/core/plugins/wordpress-playground/packages/php-wasm/universal/src/lib/php.ts:1272:13)
    at rotateRuntime (/Users/cloudnik/www/Automattic/core/plugins/wordpress-playground/packages/php-wasm/universal/src/lib/rotate-php-runtime.ts:45:14)
    at async rotateRuntimeForPhpWasmError (/Users/cloudnik/www/Automattic/core/plugins/wordpress-playground/packages/php-wasm/universal/src/lib/rotate-php-runtime.ts:64:4)

Implementation

The rotatePHPRuntime() function kills the "worn out" PHP Emscripten runtimes and replaces them with new ones. php-fpm does the same thing. Rotating the runtime happens in response to a few events emitted by the PHP class. However, rotation is an async operation and event listeners are expected to be synchronous. As a result, a PHP instance may get killed and the rotate handler will attempt to rotate it asynchronously, causing errors such as the one cited above.

This PR inlines that logic in the PHP class via a new php.enableRuntimeRotation() method. The PHP instance now keeps track if the rotation condition internally and optionally rotates the runtime before every php.run(), php.runStream(), and php.cli() call. This approach also has other benefits:

• Ability to call php.cli() and php.run() multiple times without trashing the instance – the rotation is handled internally.
• It creates a way to get rid of the primary and secondary PHP instance concept in the PHPProcessManager class. We no longer need to worry about accidentally trashing the primary instance by calling .cli() on it.
• The rotation is now lazy, not eager, and only happens on the next PHP code execution.

Potential follow-up work

• Expose a static PHP.create( runtimeFactory ) method to simplify the instance constructions. Right now you need to do const php = new PHP( runtimeId ); PHP.enableRuntimeRotation( runtimeFactory );.

Testing Instructions (or ideally a Blueprint)

CI

[adamziel]

Technically the PHP instance can still be reinitialized with another PHP runtime so it's not destroyed

[adamziel]

I inlined this call to reduce the mental load – there were too many names for me to follow

[adamziel]

@brandonpayton can you see any problems with this implementation?

[adamziel]

This is blocking other work so I'll go ahead and merge. Feel free to still leave feedback or even rollback if this ended up having any unintended consequences.