[Documentation] Replace recommonmark by myst-parser (#65664)

Recommonmark has been deprecated, then archived last year. This was
tracked by: https://github.com/llvm/llvm-iwg/issues/30

See https://github.com/readthedocs/recommonmark

This patch migrates all our doc to use myst

Additional details for bot maintainers: https://discourse.llvm.org/t/maintenance-required-on-sphinx-build-bots/73612
diff --git a/flang/docs/Intrinsics.md b/flang/docs/Intrinsics.md
index 0128b4c..ab0a940 100644
--- a/flang/docs/Intrinsics.md
+++ b/flang/docs/Intrinsics.md
@@ -8,9 +8,10 @@
 
 # A categorization of standard (2018) and extended Fortran intrinsic procedures
 
-```eval_rst
-.. contents::
-   :local:
+```{contents}
+---
+local:
+---
 ```
 
 This note attempts to group the intrinsic procedures of Fortran into categories