Reimplement and simplify Hugo's template system

See #13541 for details.

Fixes #13545
Fixes #13515
Closes #7964
Closes #13365
Closes #12988
Closes #4891

tpl/tplimpl/embedded/templates/_markup/render-image.html

@@ -0,0 +1,23 @@
+{{- $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 -}}
+<img src="{{ $src }}" alt="{{ .PlainText }}"
+  {{- with .Title }} title="{{ . }}" {{- end -}}
+  {{- range $k, $v := .Attributes -}}
+    {{- if $v -}}
+      {{- printf " %s=%q" $k ($v | transform.HTMLEscape) | safeHTMLAttr -}}
+    {{- end -}}
+  {{- end -}}
+>
+{{- /**/ -}}