Refactor getSettings to work with the mered theme

The method was loading both themes separately. This commit changes
the behavior so that it uses only the email theme which contains
also the core theme settings.
Instead of modifying the core theme settings in PHP we can now
move these settings into the email editor theme, which is merged
into the core theme.
[MAILPOET-5740]

mailpoet/lib/EmailEditor/Engine/SettingsController.php

@@ -60,19 +60,8 @@ class SettingsController {
 
   public function getSettings(): array {
     $coreDefaultSettings = get_default_block_editor_settings();
-    $coreThemeData = \WP_Theme_JSON_Resolver::get_core_data();
-    $coreSettings = $coreThemeData->get_settings();
-
-    // Email Editor Theme
     $editorTheme = $this->getTheme();
-
-    // Enable custom spacing
-    $coreSettings['spacing']['units'] = ['px'];
-    $coreSettings['spacing']['padding'] = true;
-    // Typography
-    $coreSettings['typography']['dropCap'] = false; // Showing large initial letter cannot be implemented in emails
-    $coreSettings['typography']['fontWeight'] = false; // Font weight will be handled by the font family later
-    $coreSettings['typography']['fontFamilies']['default'] = $editorTheme->get_data()['settings']['typography']['fontFamilies'];
+    $themeSettings = $editorTheme->get_settings();
 
     // body selector is later transformed to .editor-styles-wrapper
     // setting padding for bottom and top is needed because \WP_Theme_JSON::get_stylesheet() set them only for .wp-site-blocks selector
@@ -94,7 +83,7 @@ class SettingsController {
       ['css' => $flexEmailLayoutStyles],
     ];
 
-    $settings['__experimentalFeatures'] = $coreSettings;
+    $settings['__experimentalFeatures'] = $themeSettings;
     // Enable border radius, color, style and width where possible
     $settings['__experimentalFeatures']['border'] = [
       "radius" => true,

mailpoet/lib/EmailEditor/Engine/theme.json

@@ -5,7 +5,14 @@
     "layout": {
       "contentSize": "660px"
     },
+    "spacing": {
+      "units": ["px"],
+      "padding": true,
+      "margin": false
+    },
     "typography": {
+      "dropCap": false,
+      "fontWeight": false,
       "fontFamilies": [
         {
           "name": "Arial",