Implement a search link on mobile devices

Problem/Motivation

We're adding a search link to mobile devices.

Use story

As an anonymous user
I want a search link to be available on my mobile device
So that I can easily get to the search page

As a product owner of a website using CivicTheme
I want search on mobile to be available OOTB
So I don't have to customise my site to make it available

Acceptance criteria

Given I'm a site builder
When I set up my site
Then I can select whether the search link displays in the header or the menu on mobile devices

AC 1 - Link position
GIVEN I'm an anonymous user using a mobile device
WHEN I open the primary menu
THEN the search menu link and icon is available at the bottom of the menu
AND when I tap on the menu link I am taken to the search page

AC2 - Keyboard focus
GIVEN I'm an anonymous user
WHEN I use the tab key to move focus to a search input
THEN I see the button is focused using a visual indicator
THEN when I use the enter or spacebar key I am taken to the search page

AC3 - Mobile screenreader
GIVEN I'm an anonymous user
WHEN I use a mobile screenreader
AND I swipe to focus on a search input
THEN I hear its purpose is clear
AND I hear it identifies itself as a search input
AND I hear the form itself is discoverable with screenreader shortcuts as search landmark

AC4 - Site Administrator can control whether search block link appears in Mobile menu
Given I am a site administrator
When I am configuring my search block
Then I can select the search box to appear in the Mobile Menu
And the mobile menu will now contain a search link

Proposed resolution

@molecules/search/search.twig to show on mobile.
a. Remove the hide-xxs show-m-flex classes.
b. Set attributes with aria-label="Search" and check reads out correctly on screen readers.
c. In block config, place the mobile menu after search
d. Update the header theming to remove the position: absolute; top: 50%; transform: translateY(-50%); right: 0; from .ct-header .ct-mobile-navigation-trigger.

Add a field to /admin/structure/block-content/manage/civictheme_search/fields to "Show link in mobile menu".

In _civictheme_preprocess_block__civictheme_mobile_navigation:
a. Add query to get all blocks with the "Show link in mobile menu" selected
b. Use the link field in the search block to append a new link to the bottom of the mobile menu.
c. The new link added should also set an icon of magnifier.

In /mobile-navigation/mobile-navigation-menu.twig add the ability to have parameter items with an icon
a. Pass the icon parameter into the link.twig components. Icon should have a placement of before.

Add any additional styling, config or code cleanup.