Add tax rates to metadata

This doesn't do anything by itself but it lays the foundation for a solid fix for

#15895 - ie by having minimum_fee_with_tax as part of our
generally available metadata we get out of all the complexity of doing this in the js layer - which is
what is driving that bug

CRM/Member/BAO/MembershipType.php

@@ -819,6 +819,7 @@ public static function updateAllPriceFieldValue($membershipTypeId, $params) {
   public static function getAllMembershipTypes() {
     if (!Civi::cache('metadata')->has(__CLASS__ . __FUNCTION__)) {
       $types = civicrm_api3('MembershipType', 'get', ['options' => ['limit' => 0, 'sort' => 'weight']])['values'];
+      $taxRates = CRM_Core_PseudoConstant::getTaxRates();
       $keys = ['description', 'relationship_type_id', 'relationship_direction', 'max_related'];
       // In order to avoid down-stream e-notices we undo api v3 filtering of NULL values. This is covered
       // in Unit tests & ideally we might switch to apiv4 but I would argue we should build caching
@@ -832,6 +833,12 @@ public static function getAllMembershipTypes() {
         if (isset($type['contribution_type_id'])) {
           unset($types[$id]['contribution_type_id']);
         }
+        $types[$id]['tax_rate'] = (float) ($taxRates[$type['financial_type_id']] ?? 0.0);
+        $multiplier = 1;
+        if ($types[$id]['tax_git rate'] !== 0.0) {
+          $multiplier += ($types[$id]['tax_rate'] / 100);
+        }
+        $types[$id]['minimum_fee_with_tax'] = (float) $types[$id]['minimum_fee'] * $multiplier;
       }
       Civi::cache('metadata')->set(__CLASS__ . __FUNCTION__, $types);
     }

tests/phpunit/CRM/Member/BAO/MembershipTest.php

@@ -795,6 +795,8 @@ public function testBuildMembershipTypeValues() {
       'period_type' => 'rolling',
       'visibility' => 'Public',
       'weight' => '1',
+      'tax_rate' => 0.0,
+      'minimum_fee_with_tax' => 100.0,
     ], $values[1]);
   }