Fix: improve build time (#1358)

* Remove "passive" toggle

PR #1244 introduced the "passive" toggle, but just-the-docs.js subsequently disabled the only styling that used it, so it became redundant.
This removes it.

* Reduce build time for page-dependent CSS

Fix #1323

- Remove `_includes/head_nav.html`.
- Generate page-independent SCSS in `assets/css/just-the-docs-head-nav.css`.
- Link to `/assets/css/just-the-docs-head-nav.css` in `head.html`.
- Disable the above stylesheet in `assets/js/just-the-docs.js`.
- Generate page-dependent CSS in `_includes/css/activation.scss.liquid` and include in `head.html`.

* No override svg rotate

* Disable both stylesheets safely

* Move the site nav to a new include

- Fix the complete site nav
- Move the site nav to `_includes/site_nav.html`
- Cache the site nav
- Uncache `nav.html`

* Move nav and site_nav to _includes/components

* Replace id prefix

* Update breadcrumbs.html

Replace several filters by a single loop through all the pages,
but breaking as soon as possible.

Profiling indicates that this saves up to 50% of the breadcrumbs build time for the filters.

* Update just-the-docs-head-nav.css

Adjust the number of lines to keep

* Update head.html

Remove superflous type.

* Update activation.scss.liquid

Remove a superfluous closing brace.
Adjust layout.

* Use `scssify` to remove nesting

Preliminary profiling indicates that using `scssify` on the small number of nested CSS rules produced by `activation.scss.liquid` is quick enough.

* Update head.scss

Manual attempt at prettier (pending installation in Atom).

* Avoid generation of nested CSS

Local profiling indicated that using `scssify` on each page takes about 1% of the build time.

- Update `_includes/css/activation.scss.liquid` to generate non-nested CSS.
- Remove use of `scssify` from `_includes/head.html`.

* Ignore false positives from validator

Ignores: `:1.810-1.823: error: CSS: Parse Error.` and `:1.811-1.824: error: CSS: Parse Error.`; had to shift things around since the local config overrides the CI flag.

* Inline `_sass/head.css`

* Update CHANGELOG.md

---------

Co-authored-by: Matthew Wang <matt@matthewwang.me>

_includes/components/breadcrumbs.html

@@ -3,30 +3,38 @@
   Depends on: page, site.
   Results in: HTML for the breadcrumbs component.
   Overwrites:
-    pages_list, parent_page, grandparent_page.
+    node, pages_list, parent_page, grandparent_page.
 {%- endcomment -%}
 
 {%- if page.url != "/" and page.parent -%}
 
-  {%- assign pages_list = site[page.collection]
-      | default: site.html_pages
-      | where_exp: "item", "item.title != nil"
-      | where_exp: "item", "item.has_children != nil" -%}
+  {%- assign pages_list = site[page.collection] | default: site.html_pages -%}
 
-  {%- if page.grand_parent -%}
-    {%- assign parent_page = pages_list
-        | where: "title", page.parent
-        | where: "parent", page.grand_parent
-        | first -%}
-    {%- assign grandparent_page = pages_list
-        | where: "title", page.grand_parent
-        | first -%}
-  {%- else -%}
-    {%- assign parent_page = pages_list
-        | where: "title", page.parent
-        | where_exp: "item", "item.parent == nil"
-        | first -%}
-  {%- endif -%}
+  {%- assign parent_page = nil -%}
+  {%- assign grandparent_page = nil -%}
+
+  {%- for node in pages_list -%}
+  
+    {%- if node.has_children and page.grand_parent -%}
+
+      {%- if node.title == page.parent and node.parent == page.grand_parent -%}
+        {%- assign parent_page = node -%}
+      {%- endif -%}
+      {%- if node.title ==  page.grand_parent -%}
+        {%- assign grandparent_page = node -%}
+      {%- endif -%}
+      {%- if parent_page and grandparent_page -%}
+        {%- break -%}
+      {%- endif -%}
+
+    {%- elsif node.has_children and node.title == page.parent and node.parent == nil -%}
+
+      {%- assign parent_page = node -%}
+      {%- break -%}
+
+    {%- endif -%}
+
+  {%- endfor -%}
 
 <nav aria-label="Breadcrumb" class="breadcrumb-nav">
   <ol class="breadcrumb-nav-list">