theme check visible_if on paragraph is valid (#997)

### TL;DR

Added `visible_if` property to paragraph type settings in theme schema.

### What changed?

Added the `visible_if` property to the paragraph type settings in the theme schema JSON file. This allows paragraph elements to be conditionally displayed based on other setting values.

### How to test?

1. Create a theme setting with a paragraph type that includes a `visible_if` condition
2. Verify that the paragraph is only displayed when the condition is met
3. Test with different condition values to ensure proper visibility toggling

### Why make this change?

Conditionally show or hide paragraph elements in the theme settings and validation accurately reflects for paragraph

Author: stephanie-shopify

schemas/theme/setting.json

@@ -1133,7 +1133,8 @@
           "description": "A setting of type paragraph outputs a text element to help you better describe your input settings.",
           "markdownDescription": "A setting of type `paragraph` outputs a text element to help you better describe your input settings.\n\n---\n\n[Shopify reference](https://shopify.dev/docs/themes/architecture/settings/sidebar-settings#paragraph)"
         },
-        "content": true
+        "content": true,
+        "visible_if": true
       },
       "additionalProperties": false
     },