Add PHP unit tests and page tests.

Run "composer install", then "composer test".

tests/php/Support/FakeResult.php

@@ -0,0 +1,27 @@
+<?php
+namespace Xxx\Tests\Support;
+
+// The result of a FakeDb query
+class FakeResult {
+  private array $rows;
+  private int $next = 0;
+  public int $num_rows;
+
+  public function __construct(array $rows) {
+    $this->rows = array_values($rows);
+    $this->num_rows = count($this->rows);
+  }
+
+  public function fetch_assoc() {
+    return $this->rows[$this->next++] ?? NULL;
+  }
+
+  public function fetch_row() {
+    $row = $this->fetch_assoc();
+    return $row === NULL ? NULL : array_values($row);
+  }
+
+  public function close() {
+    return TRUE;
+  }
+}