[ui5-menu-item]: Incorrect spelling of ui5-menu-rp-sub-menu class

[dimovpetar]

In MenuItemTemplate.tsx, ui5-menu-rp-sub-menu class is written with leading dot, which is incorrect. As a results, some CSS selectors depending on this class are ineffective.

ui5-webcomponents/packages/main/src/MenuItemTemplate.tsx

Line 81 in 078d44c

class="ui5-menu-rp .ui5-menu-rp-sub-menu"

After the fix, test if the following styles, located in MenuItem.css, are needed:

.ui5-menu-rp.ui5-menu-rp-sub-menu {
	margin-top: 0.25rem;
	margin-inline: var(--_ui5_menu_submenu_margin_offset);
}

.ui5-menu-rp.ui5-menu-rp-sub-menu[actual-placement="Start"] {
	margin-top: 0.25rem;
	margin-inline: var(--_ui5_menu_submenu_placement_type_left_margin_offset);
}