Docs: Allow unlimited multi-level navigation (#1440)

* Remove `jekyll-default-layout` plugin

* Move docs/navigation-structure to docs/navigation

* Fix uses of line-nos in md files

* Update CHANGELOG.md

---------

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

docs/ui-components/buttons.md

@@ -1,5 +1,4 @@
 ---
-layout: default
 title: Buttons
 parent: UI Components
 nav_order: 2

docs/ui-components/callouts.md

@@ -1,5 +1,4 @@
 ---
-layout: default
 title: Callouts
 parent: UI Components
 nav_order: 7

docs/ui-components/code/index.md

@@ -1,8 +1,6 @@
 ---
-layout: default
 title: Code
 parent: UI Components
-has_children: true
 nav_order: 6
 ---
 
@@ -58,7 +56,7 @@ var fun = function lang(l) {
 ```
 {% endhighlight %}
 
-Syntax highlighting, line numbers, and HTML compression do not work together; **the combination of these features generates invalid HTML that renders incorrectly**. To learn more, see ["Code with line numbers"]({% link docs/ui-components/line-nos.md %}).
+Syntax highlighting, line numbers, and HTML compression do not work together; **the combination of these features generates invalid HTML that renders incorrectly**. To learn more, see ["Code with line numbers"]({% link docs/ui-components/code/line-numbers.md %}).
 
 ---
 

docs/ui-components/code/line-numbers.md

@@ -1,15 +1,11 @@
 ---
-layout: default
-title: Code with line numbers
+title: Line Numbers
 parent: Code
-grand_parent: UI Components
-permalink: /docs/ui-components/code/line-numbers/
 ---
 
-# Code snippets with line numbers
+# Code Snippets with Line Numbers
 
 {: .warning }
-
 In prior versions of the docs, we provided "workarounds" to rendering issues arising from code snippets with line numbers. While these seemed to resolve visual layout issues, they did not resolve core issues with Jekyll generating invalid HTML. See [the detailed explanation](#detailed-error-explanation) for more information.
 
 The default settings for HTML compression are incompatible with the HTML

docs/ui-components/index.md

@@ -1,9 +1,6 @@
 ---
-layout: default
 title: UI Components
 nav_order: 3
-has_children: true
-permalink: /docs/ui-components
 ---
 
 # UI Components

docs/ui-components/labels.md

@@ -1,5 +1,4 @@
 ---
-layout: default
 title: Labels
 parent: UI Components
 nav_order: 3

docs/ui-components/lists.md

@@ -1,5 +1,4 @@
 ---
-layout: default
 title: Lists
 parent: UI Components
 nav_order: 5

docs/ui-components/tables.md

@@ -1,5 +1,4 @@
 ---
-layout: default
 title: Tables
 parent: UI Components
 nav_order: 4

docs/ui-components/typography.md

@@ -1,5 +1,4 @@
 ---
-layout: default
 title: Typography
 parent: UI Components
 nav_order: 1