Implement new template system added with Hugo v0.146.0 (#1858)

* feat(layouts): move all files in layouts/_default up to the layouts/ root.

* feat(layouts): rename layouts/partials folder to layouts/_partials

* feat(layouts): rename layouts/shortcodes folder to layouts/_shortcodes

* feat(taxonomy): add new taxonomy layout template

A template named taxonomy.html used to be a candidate for both Page kind term and taxonomy, now it’s only considered for taxonomy.

layouts/_markup/render-image.html

@@ -0,0 +1,22 @@
+{{- $u := urls.Parse .Destination -}}
+{{- $src := $u.String -}}
+{{- if not $u.IsAbs -}}
+  {{- $path := strings.TrimPrefix "./" $u.Path }}
+  {{- with or (.PageInner.Resources.Get $path) (resources.Get $path) -}}
+    {{- $src = .RelPermalink -}}
+    {{- with $u.RawQuery -}}
+      {{- $src = printf "%s?%s" $src . -}}
+    {{- end -}}
+    {{- with $u.Fragment -}}
+      {{- $src = printf "%s#%s" $src . -}}
+    {{- end -}}
+  {{- end -}}
+{{- end -}}
+{{- $attributes := merge .Attributes (dict "alt" .Text "src" $src "title" (.Title | transform.HTMLEscape) "loading" "lazy") -}}
+<img
+  {{- range $k, $v := $attributes -}}
+    {{- if $v -}}
+      {{- printf " %s=%q" $k $v | safeHTMLAttr -}}
+    {{- end -}}
+  {{- end -}}>
+{{- /**/ -}}