Block categories - ensure that categories are unique by slug. (#62954)

* blocks/store/reducer // ensure that categories are unique by slug.

Block categories can be registered through backend by hooking into the "block_categories_all"-filter or through frontend by calling wp.blocks.setCategories(). Both require an array of WPBlockCategory elements. This change aims for making the categories: WPBlockCategory[] with unique entries by slug to avoid rendering in Block Inserter all Blocks duplicated.

See also: #50061

* eslint

* blocks/store/reducer.js // add test case for unique catgories by slug.

----

Co-authored-by: Chrico <chrico@git.wordpress.org>
Co-authored-by: talldan <talldanwp@git.wordpress.org>

packages/blocks/src/store/reducer.js

@@ -328,7 +328,12 @@ export const groupingBlockName = createBlockNameSetterReducer(
 export function categories( state = DEFAULT_CATEGORIES, action ) {
 	switch ( action.type ) {
 		case 'SET_CATEGORIES':
-			return action.categories || [];
+			// Ensure, that categories are unique by slug.
+			const uniqueCategories = new Map();
+			( action.categories || [] ).forEach( ( category ) => {
+				uniqueCategories.set( category.slug, category );
+			} );
+			return [ ...uniqueCategories.values() ];
 		case 'UPDATE_CATEGORY': {
 			if (
 				! action.category ||

packages/blocks/src/store/test/reducer.js

@@ -420,6 +420,22 @@ describe( 'categories', () => {
 		expect( state ).toEqual( [ { slug: 'wings', title: 'Wings' } ] );
 	} );
 
+	it( 'should ensure, that categories are unique by slug', () => {
+		const original = deepFreeze( [
+			{ slug: 'chicken', title: 'Chicken' },
+		] );
+
+		const state = categories( original, {
+			type: 'SET_CATEGORIES',
+			categories: [ { slug: 'chicken', title: 'Another chicken' } ],
+		} );
+
+		expect( state ).toEqual( [
+			{ slug: 'chicken', title: 'Another chicken' },
+		] );
+		expect( state.length ).toBe( 1 );
+	} );
+
 	it( 'should add the category icon', () => {
 		const original = deepFreeze( [
 			{