MDL-70296 core: Update the moodle's readme, xml and upgrade files

lib/markdown/readme_moodle.txt

@@ -5,15 +5,11 @@ Procedure:
 * copy the classes and readme file to lib/markdown/* , Note .inc files need not be copied.
 * update function markdown_to_html() in weblib.php if necessary,
   note that we require the php files manually for performance reasons
-* reapply the following commit if it's not present in the release we are upgrading to:
-      https://github.com/michelf/php-markdown/commit/a35858f0409e5f01474f5cd562d17289fe8e5435
-      (if there is any problem you can, alternatively, reapply MDL-66964 php fix commit itself))
-  (revove this step once the release includes the commit)
-
 * run phpunit tests (all PHP versions)
 
 Petr Skoda
 
-* Currently using the 1.8.0 release + (php74 fixup commit)
+* Removed fixup step in procedure
+* Currently using the 1.9.0 release(includes php74 fixup commit)
 
-Mathew May
+Peter Dias

lib/thirdpartylibs.xml

@@ -163,9 +163,9 @@
   </library>
   <library>
     <location>markdown</location>
-    <name>Markdown original+extra</name>
+    <name>Markdown original</name>
     <license>BSD</license>
-    <version>1.8.0</version>
+    <version>1.9.0</version>
     <licenseversion></licenseversion>
   </library>
   <library>

lib/upgrade.txt

@@ -15,6 +15,7 @@ information provided here is intended especially for developers.
 * Behat timeout constants behat_base::TIMEOUT, EXTENDED_TIMEOUT, and REDUCED_TIMEOUT, which were deprecated in 3.7, have been removed.
 * \core_table\local\filter\filterset::JOINTYPE_DEFAULT is being changed from 1 (ANY) to 2 (ALL). Filterset implementations
   can override the default filterset join type by overriding \core_table\local\filter\filterset::get_join_type() instead.
+* Markdown lib has been upgraded to the latest version - 1.9.0
 
 === 3.10 ===
 * PHPUnit has been upgraded to 8.5. That comes with a few changes: