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-codeblock-goat.html

@@ -0,0 +1,18 @@
+{{ $width := .Attributes.width }}
+{{ $height := .Attributes.height }}
+{{ $class := .Attributes.class | default "" }}
+<div class="goat svg-container {{ $class }}">
+  {{ with diagrams.Goat .Inner }}
+    <svg
+      xmlns="http://www.w3.org/2000/svg"
+      font-family="Menlo,Lucida Console,monospace"
+      {{ if or $width $height }}
+        {{ with $width }}width="{{ . }}"{{ end }}
+        {{ with $height }}height="{{ . }}"{{ end }}
+      {{ else }}
+        viewBox="0 0 {{ .Width }} {{ .Height }}"
+      {{ end }}>
+      {{ .Inner }}
+    </svg>
+  {{ end }}
+</div>

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 -}}
+>
+{{- /**/ -}}

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

@@ -0,0 +1,22 @@
+{{- $u := urls.Parse .Destination -}}
+{{- $href := $u.String -}}
+{{- if strings.HasPrefix $u.String "#" -}}
+  {{- $href = printf "%s#%s" .PageInner.RelPermalink $u.Fragment -}}
+{{- else if and $href (not $u.IsAbs) -}}
+  {{- $path := strings.TrimPrefix "./" $u.Path -}}
+  {{- with or
+    ($.PageInner.GetPage $path)
+    ($.PageInner.Resources.Get $path)
+    (resources.Get $path)
+  -}}
+    {{- $href = .RelPermalink -}}
+    {{- with $u.RawQuery -}}
+      {{- $href = printf "%s?%s" $href . -}}
+    {{- end -}}
+    {{- with $u.Fragment -}}
+      {{- $href = printf "%s#%s" $href . -}}
+    {{- end -}}
+  {{- end -}}
+{{- end -}}
+<a href="{{ $href }}" {{- with .Title }} title="{{ . }}" {{- end }}>{{ .Text }}</a>
+{{- /**/ -}}

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

@@ -0,0 +1,37 @@
+<table
+  {{- range $k, $v := .Attributes }}
+    {{- if $v }}
+      {{- printf " %s=%q" $k ($v | transform.HTMLEscape) | safeHTMLAttr }}
+    {{- end }}
+  {{- end }}>
+  <thead>
+    {{- range .THead }}
+      <tr>
+        {{- range . }}
+          <th
+            {{- with .Alignment }}
+              {{- printf " style=%q" (printf "text-align: %s" .) | safeHTMLAttr }}
+            {{- end -}}
+          >
+            {{- .Text -}}
+          </th>
+        {{- end }}
+      </tr>
+    {{- end }}
+  </thead>
+  <tbody>
+    {{- range .TBody }}
+      <tr>
+        {{- range . }}
+          <td
+            {{- with .Alignment }}
+              {{- printf " style=%q" (printf "text-align: %s" .) | safeHTMLAttr }}
+            {{- end -}}
+          >
+            {{- .Text -}}
+          </td>
+        {{- end }}
+      </tr>
+    {{- end }}
+  </tbody>
+</table>