Add template for header search separate from navbar search

It didn't look as good bouncing up and down in the middle of the page.

Also, style it to be a bit longer.

agaric/sass/agaric/_component.titlebar.scss

@@ -51,3 +51,7 @@
 .titlebar + .byline {
   margin-top: 1.5rem;
 }
+
+.header-search .form-text.input {
+  width: 25em;
+}

agaric/templates/block/block--header-search.html.twig

@@ -0,0 +1,32 @@
+{#
+/**
+ * @file
+ * Theme override to display a block.
+ *
+ * Available variables:
+ * - plugin_id: The ID of the block implementation.
+ * - label: The configured label of the block if visible.
+ * - configuration: A list of the block's configuration values.
+ *   - label: The configured label for the block.
+ *   - label_display: The display settings for the label.
+ *   - provider: The module or other provider that provided this block plugin.
+ *   - Block plugin specific settings will also be stored here.
+ * - content: The content of this block.
+ * - attributes: array of HTML attributes populated by modules, intended to
+ *   be added to the main container tag of this template.
+ *   - id: A valid HTML ID and guaranteed unique.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
+ * - title_prefix: Additional output populated by modules, intended to be
+ *   displayed in front of the main title tag that appears in the template.
+ * - title_suffix: Additional output populated by modules, intended to be
+ *   displayed after the main title tag that appears in the template.
+ *
+ * @see template_preprocess_block()
+ */
+#}
+<div{{ attributes.addClass('header-search') }}>
+  {% block content %}
+    {{ content }}
+  {% endblock %}
+</div>

agaric/templates/layout/page.html.twig

@@ -61,9 +61,10 @@
       {% else %}
         <div class="titlebar">
           {{ page.header }}
-          {% if page.secondary_menu %}
+          {% if page.secondary_menu or page.header_search %}
             <div class="titlebar_links">
               {{ page.secondary_menu }}
+              {{ page.header_search }}
             </div>
           {% endif %}
         </div>