Add attribute so Nav Editor can hide justify

- Adds an additional attribute to showJustifyControls to navigation
block so the Nav Editor screen can hide the controls, since that screen
is intended to create/edit nav menus and not format/style.

- Use 'showJustifyControls' since the positive is easier to reason and
there is already a 'showSubMenuIcon' attribute that also defaults to
true

packages/block-library/src/navigation/block.json

@@ -30,6 +30,10 @@
 		"showSubmenuIcon": {
 			"type": "boolean",
 			"default": true
+		},
+		"showJustifyControls": {
+			"type": "boolean",
+			"default": true
 		}
 	},
 	"providesContext": {
@@ -40,6 +44,7 @@
 		"fontSize": "fontSize",
 		"customFontSize": "customFontSize",
 		"showSubmenuIcon": "showSubmenuIcon",
+		"showJustifyControls": "showJustifyControls",
 		"style": "style",
 		"orientation": "orientation"
 	},

packages/block-library/src/navigation/edit.js

@@ -119,17 +119,19 @@ function Navigation( {
 	return (
 		<>
 			<BlockControls>
-				<JustifyToolbar
-					value={ attributes.itemsJustification }
-					allowedControls={ justifyAllowedControls }
-					onChange={ ( value ) =>
-						setAttributes( { itemsJustification: value } )
-					}
-					popoverProps={ {
-						position: 'bottom right',
-						isAlternate: true,
-					} }
-				/>
+				{ attributes.showJustifyControls && (
+					<JustifyToolbar
+						value={ attributes.itemsJustification }
+						allowedControls={ justifyAllowedControls }
+						onChange={ ( value ) =>
+							setAttributes( { itemsJustification: value } )
+						}
+						popoverProps={ {
+							position: 'bottom right',
+							isAlternate: true,
+						} }
+					/>
+				) }
 				<ToolbarGroup>{ navigatorToolbarButton }</ToolbarGroup>
 			</BlockControls>
 			{ navigatorModal }