extension-compatibility - Add 'force-uninstall' mode for api4 transition

There is a compatibility problem when upgrading a system which  has an old
copy of api4: the top level `api4.php` indiscriminately declares the
function `civicrm_api4()`, which eventually provokes a conflict with the
copy that is now in `civicrm-core`.

Using the normal disable/uninstall actions doesn't resolve this because the
error arises too early during boot (before the upgrader gets a chance to
remove the extension).

The 'force-uninstall' option will make the system behave as if the extension
is uninstalled, regardless of what files exist and what state may be stored
in the `civicrm_extension` table.

This commit technically does ~3 things:

1. Changes the policy for `org.civicrm.api4` to use `force-uninstall`
2. Makes the extension-cache version-dependent. During an upgrade, you
   might have a stale cache that claims that the old extension is
   active. This ensures that (as soon as you drop in new code)
   it begins working with a fresh cache.
3. Update any spots which query the table `civicrm_extensions` for
   extension status. Have it consult `extension-compatibility.json`
   for `force-uninstall`ed items.

CRM/Core/PseudoConstant.php

@@ -1454,6 +1454,7 @@ WHERE  id = %1
    */
   public static function &getExtensions() {
     if (!self::$extensions) {
+      $compat = CRM_Extension_System::getCompatibilityInfo();
       self::$extensions = [];
       $sql = '
         SELECT full_name, label
@@ -1462,6 +1463,9 @@ WHERE  id = %1
       ';
       $dao = CRM_Core_DAO::executeQuery($sql);
       while ($dao->fetch()) {
+        if (!empty($compat[$dao->full_name]['force-uninstall'])) {
+          continue;
+        }
         self::$extensions[$dao->full_name] = $dao->label;
       }
     }

CRM/Extension/Manager.php

@@ -465,6 +465,8 @@ class CRM_Extension_Manager {
    */
   public function getStatuses() {
     if (!is_array($this->statuses)) {
+      $compat = CRM_Extension_System::getCompatibilityInfo();
+
       $this->statuses = [];
 
       foreach ($this->fullContainer->getKeys() as $key) {
@@ -484,7 +486,10 @@ class CRM_Extension_Manager {
         catch (CRM_Extension_Exception $e) {
           $codeExists = FALSE;
         }
-        if ($dao->is_active) {
+        if (!empty($compat[$dao->full_name]['force-uninstall'])) {
+          $this->statuses[$dao->full_name] = self::STATUS_UNINSTALLED;
+        }
+        elseif ($dao->is_active) {
           $this->statuses[$dao->full_name] = $codeExists ? self::STATUS_INSTALLED : self::STATUS_INSTALLED_MISSING;
         }
         else {

CRM/Extension/Mapper.php

@@ -286,6 +286,8 @@ class CRM_Extension_Mapper {
     }
 
     if (!is_array($moduleExtensions)) {
+      $compat = CRM_Extension_System::getCompatibilityInfo();
+
       // Check canonical module list
       $moduleExtensions = [];
       $sql = '
@@ -296,6 +298,9 @@ class CRM_Extension_Mapper {
       ';
       $dao = CRM_Core_DAO::executeQuery($sql);
       while ($dao->fetch()) {
+        if (!empty($compat[$dao->full_name]['force-uninstall'])) {
+          continue;
+        }
         try {
           $moduleExtensions[] = [
             'prefix' => $dao->file,

CRM/Extension/System.php

@@ -264,7 +264,7 @@ class CRM_Extension_System {
    */
   public function getCache() {
     if ($this->cache === NULL) {
-      $cacheGroup = md5(serialize(['ext', $this->parameters]));
+      $cacheGroup = md5(serialize(['ext', $this->parameters, CRM_Utils_System::version()]));
       // Extension system starts before container. Manage our own cache.
       $this->cache = CRM_Utils_Cache::create([
         'name' => $cacheGroup,

extension-compatibility.json

 {
   "org.civicrm.api4": {
     "obsolete": "5.19",
-    "disable": true,
-    "uninstall": true
+    "force-uninstall": true
   },
   "uk.squiffle.kam": {
     "obsolete": "5.12",