Move FFI functions to a separate class (libvips#147)

* Move FFI functions to a separate class

* Ensure libvips can be found on Apple Silicon

Allow users to set the `VIPSHOME` env when libvips is installed in a
non-standard path. On macOS, always search in `/opt/homebrew/lib/`
as a fallback.

In most cases, either the `LD_LIBRARY_PATH` or `DYLD_LIBRARY_PATH`
env is preferred. On macOS, however, that no longer works since
Apple introduced System Integrity Protection (SIP).

See: libvips#140.

* Prefer the strict equality operator

Author: kleisauke

src/Config.php

@@ -54,8 +54,8 @@ class Exception extends \Exception
     public function __construct($message = "", $code = 0, \Throwable $previous = null)
     {
         if ($message == "") {
-            $message = "libvips error: " . Config::vips()->vips_error_buffer();
-            Config::vips()->vips_error_clear();
+            $message = "libvips error: " . FFI::vips()->vips_error_buffer();
+            FFI::vips()->vips_error_clear();
         }
 
         Utils::errorLog($message);