Implement escaping in src (org only) and example blocks

inside src example blocks lines starting with `\s*,` are escaped - i.e. org
mode will not try to parse them as e.g. a headline. We don't want to render the
escape commata to html so let's take them out - and put them back in before
rendering to org. Doing it this way allows us to render them correctly even
when the input did not include them.

see https://orgmode.org/manual/Literal-Examples.html#Literal-Examples

org/testdata/blocks.html

@@ -96,6 +96,24 @@ paragraphs
 </li>
 </ul>
 </blockquote>
+<div class="src src-org">
+<div class="highlight">
+<pre>
+  #+BEGIN_SRC bash
+  echo src (with language org) and example blocks support escaping using commata
+  #+END_SRC
+
+,* I am not a real headline - commata escape characters aren&#39;t renderered
+</pre>
+</div>
+</div>
+<pre class="example">
+  #+BEGIN_SRC bash
+  echo src (with language org) and example blocks support escaping using commata
+  #+END_SRC
+
+,* I am not a real headline - commata escape characters aren&#39;t renderered
+</pre>
 <script>
 console.log("Hello World!")
 </script>

org/testdata/blocks.org

@@ -51,6 +51,23 @@ blocks like the quote block parse their content and can contain
         it can be made visible using css (e.g. =white-space: pre=).
 #+END_QUOTE
 
+#+BEGIN_SRC org
+  ,#+BEGIN_SRC bash
+  echo src (with language org) and example blocks support escaping using commata
+  ,#+END_SRC
+
+,,* I am not a real headline - commata escape characters aren't renderered
+
+#+END_SRC
+
+#+BEGIN_EXAMPLE
+  ,#+BEGIN_SRC bash
+  echo src (with language org) and example blocks support escaping using commata
+  ,#+END_SRC
+
+,,* I am not a real headline - commata escape characters aren't renderered
+#+END_EXAMPLE
+
 #+BEGIN_EXPORT html
 <script>
 console.log("Hello World!")

org/testdata/blocks.pretty_org

@@ -51,6 +51,23 @@ blocks like the quote block parse their content and can contain
         it can be made visible using css (e.g. =white-space: pre=).
 #+END_QUOTE
 
+#+BEGIN_SRC org
+  ,#+BEGIN_SRC bash
+  echo src (with language org) and example blocks support escaping using commata
+  ,#+END_SRC
+
+,,* I am not a real headline - commata escape characters aren't renderered
+
+#+END_SRC
+
+#+BEGIN_EXAMPLE
+  ,#+BEGIN_SRC bash
+  echo src (with language org) and example blocks support escaping using commata
+  ,#+END_SRC
+
+,,* I am not a real headline - commata escape characters aren't renderered
+#+END_EXAMPLE
+
 #+BEGIN_EXPORT html
 <script>
 console.log("Hello World!")
@@ -80,7 +97,7 @@ this unindented line is outside of the list item
 
   #+BEGIN_QUOTE
   #+BEGIN_EXAMPLE
-  #+END_QUOTE
+  ,#+END_QUOTE
   #+END_EXAMPLE
   #+END_QUOTE