MDL-72837 core_cache: Add versioned cache support

Adds new set_versioned and get_versioned APIs to cache, which means you can
request a specific version from cache and it will not return an outdated
version.

This is important when using multi-layer-caches where a local cache might have
an outdated version of the cache, but the shared cache has a current version.
With this feature, the content of the cache does not have to be rebuilt, as
it will automatically retrieve it from the shared cache if necessary.

cache/disabledlib.php

@@ -61,14 +61,27 @@ class cache_disabled extends cache {
      * Gets a key from the cache.
      *
      * @param int|string $key
+     * @param int $requiredversion Minimum required version of the data or cache::VERSION_NONE
      * @param int $strictness Unused.
+     * @param mixed &$actualversion If specified, will be set to the actual version number retrieved
      * @return bool
      */
-    public function get($key, $strictness = IGNORE_MISSING) {
-        if ($this->get_datasource() !== false) {
-            return $this->get_datasource()->load_for_cache($key);
+    protected function get_implementation($key, int $requiredversion, int $strictness, &$actualversion = null) {
+        $datasource = $this->get_datasource();
+        if ($datasource !== false) {
+            if ($requiredversion === cache::VERSION_NONE) {
+                return $datasource->load_for_cache($key);
+            } else {
+                if (!$datasource instanceof cache_data_source_versionable) {
+                    throw new \coding_exception('Data source is not versionable');
+                }
+                $result = $datasource->load_for_cache_versioned($key, $requiredversion, $actualversion);
+                if ($result && $actualversion < $requiredversion) {
+                    throw new \coding_exception('Data source returned outdated version');
+                }
+                return $result;
+            }
         }
-
         return false;
     }
 
@@ -91,10 +104,12 @@ class cache_disabled extends cache {
      * Sets a key value pair in the cache.
      *
      * @param int|string $key Unused.
+     * @param int $version Unused.
      * @param mixed $data Unused.
+     * @param bool $setparents Unused.
      * @return bool
      */
-    public function set($key, $data) {
+    protected function set_implementation($key, int $version, $data, bool $setparents = true): bool {
         return false;
     }