Factor out construction of font-related JSON schemas (#15341)

This PR factors out the construction of the font-related JSON schemas,
as they were used in multiple places.

Release Notes:

- N/A

crates/settings/src/json_schema.rs

@@ -1,4 +1,39 @@
-use schemars::schema::{RootSchema, Schema};
+use schemars::schema::{ArrayValidation, InstanceType, RootSchema, Schema, SchemaObject};
+use serde_json::Value;
+
+pub struct SettingsJsonSchemaParams<'a> {
+    pub staff_mode: bool,
+    pub language_names: &'a [String],
+    pub font_names: &'a [String],
+}
+
+impl<'a> SettingsJsonSchemaParams<'a> {
+    pub fn font_family_schema(&self) -> Schema {
+        let available_fonts: Vec<_> = self.font_names.iter().cloned().map(Value::String).collect();
+
+        SchemaObject {
+            instance_type: Some(InstanceType::String.into()),
+            enum_values: Some(available_fonts),
+            ..Default::default()
+        }
+        .into()
+    }
+
+    pub fn font_fallback_schema(&self) -> Schema {
+        SchemaObject {
+            instance_type: Some(InstanceType::Array.into()),
+            array: Some(Box::new(ArrayValidation {
+                items: Some(schemars::schema::SingleOrVec::Single(Box::new(
+                    self.font_family_schema(),
+                ))),
+                unique_items: Some(true),
+                ..Default::default()
+            })),
+            ..Default::default()
+        }
+        .into()
+    }
+}
 
 type PropertyName<'a> = &'a str;
 type ReferencePath<'a> = &'a str;