fix(ui): blocks field not respecting width styles in row layouts (#13502)

### What?

This PR applies `mergeFieldStyles` to the `BlocksField` component,
ensuring that custom admin styles such as `width` are correctly
respected when Blocks fields are placed inside row layouts.

### Why?

Previously, Blocks fields did not inherit or apply their `admin.width`
(or other merged field styles). For example, when placing two Blocks
fields side by side inside a row with `width: '50%'`, the widths were
ignored, causing layout issues.

### How?

- Imported and used `mergeFieldStyles` within `BlocksField`.
- Applied the merged styles to the root `<div>` via the `style` prop,
consistent with how other field components (like `TextField`) handle
styles.

Fixes #13498

test/fields/payload-types.ts

@@ -1129,6 +1129,22 @@ export interface RowField {
   no_set_width_within_row_b?: string | null;
   no_set_width_within_row_c?: string | null;
   field_20_percent_width_within_row_d?: string | null;
+  leftColumn?:
+    | {
+        leftText?: string | null;
+        id?: string | null;
+        blockName?: string | null;
+        blockType: 'leftTextBlock';
+      }[]
+    | null;
+  rightColumn?:
+    | {
+        rightText?: string | null;
+        id?: string | null;
+        blockName?: string | null;
+        blockType: 'rightTextBlock';
+      }[]
+    | null;
   updatedAt: string;
   createdAt: string;
 }
@@ -2760,6 +2776,28 @@ export interface RowFieldsSelect<T extends boolean = true> {
   no_set_width_within_row_b?: T;
   no_set_width_within_row_c?: T;
   field_20_percent_width_within_row_d?: T;
+  leftColumn?:
+    | T
+    | {
+        leftTextBlock?:
+          | T
+          | {
+              leftText?: T;
+              id?: T;
+              blockName?: T;
+            };
+      };
+  rightColumn?:
+    | T
+    | {
+        rightTextBlock?:
+          | T
+          | {
+              rightText?: T;
+              id?: T;
+              blockName?: T;
+            };
+      };
   updatedAt?: T;
   createdAt?: T;
 }