doc, module: change async customization hooks to experimental

There is ongoing work to replace async customization hooks by a
synchronous variant.
As a result bugs/design flaws or the async variant (thread leak,
overhead) are not addressed.
Adapt stability index to avoid wrong assumptions they might move to
stable.

Refs: nodejs/loaders#201
Refs: nodejs/loaders#198
PR-URL: #60302
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Jacob Smith <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Marco Ippolito <[email protected]>
Reviewed-By: Darshan Sen <[email protected]>

Author: Flarna

doc/api/module.md

@@ -572,8 +572,7 @@ changes:
 
 <!-- type=misc -->
 
-> Stability: 1.2 - Release candidate (asynchronous version)
-> Stability: 1.1 - Active development (synchronous version)
+> Stability: 1.1 - Active development
 
 There are two types of module customization hooks that are currently supported: