Add search block(s) to the header

Here's a suggestion of how we could lay out the regions (header, primary_menu, and secondary_menu) in page.html.twig. The crux is that the search block form needs different markup based on which region it gets placed into. I think we can use template suggestions to make that work. As a fallback, we could make a separate region just called "Search" and then print it twice, once in each place where it's needed with different wrappers.

FYI, here's some sample code for adding region-specific block suggestions, if we decide to go that route (adapted from Twig Suggest):

/**
 * Implements hook_theme_suggestions_HOOK_alter() for block().
 */
function olivero_theme_suggestions_block_alter(&$suggestions, array $variables) {

  // Add region-specific block theme suggestions.
  // Prevent PHP notices if contrib modules create blocks without this ID.
  if (isset($variables['elements']['#id']) || !empty($variables['elements']['#id'])) {

    // @todo Use entity storage instead of Block class.
    $block = \Drupal\block\Entity\Block\Block::load($variables['elements']['#id']);

    $suggestions[] = 'block__' . $block->getRegion();
    $suggestions[] = 'block__' . $block->getRegion() . '__' . $variables['elements']['#id'];
  }
}

Here's a PoC for adding search markup according to theme settings, represented by the olivero template variable that doesn't currently exist, rather than the search block(s).

Updating if statements to consider search setting.

Next up: I'll tackle preprocessing the search form markup by the end of the week.

Last patch had twig error. this one fixes that and uses the page.header_search variable from #3115429: Create theme settings for mobile menu

Thanks for adding that header_search theme setting, @mrconnorton :) I've added a page preprocess that uses the setting here in this patch, so I'll submit a change to the other issue to take it out of the html preprocess.

Re-roll against latest HEAD.

@mherchel, I noticed that the <div class="secondary-nav__wrapper"> wrapper was removed from page.html.twig. I've added it back here in this patch, but if the deletion was intentional, lemme know and I'll take it out.

(bad patch)

Here's a patch to demonstrate a block-based approach as opposed to using theme-settings and loading the search form in hook_preprocess_page().

Sure! I'll make new versions of each patch with this added in via hook_form_alter().

I forgot to include a few files in the last patch. Here it is again, and with @mherchel's requested changes to the search form submit button markup.

This version of the patch is for the block-based (and IMO preferred) approach.

Here's an updated version of the theme settings-based approach, with @mherchel's requested changes added in to change inputs to buttons.

Updating patch from #16 as I forgot to include a file.

Updated block-based approach patch from #15 (improved twig file comment).

Hides block labels.

@hawkeye.twolf Thanks for submitting this patch! I just tested your patch and made some minor adjustments, but the two search blocks (narrow and wide) are looking great! https://git.drupalcode.org/project/olivero/-/commit/10e9c47595f07aacc97e...

See the latest tugboat preview here - https://8-x-1-x-dev-2t4d1epwkj8tgwxduizmixhzevqwzi8w.tugboat.qa/

Also, we'll need to render the search form placeholder text and move the search icon to be inline SVG, but we'll take of that in another ticket. Thanks for all of your help in this again!