Document Sketcher internal face fixes

[er1c-cartman]

Summary:
Adds a FreeCAD 1.2 release-note entry for FreeCAD/FreeCAD#28964.

Related bounty or issue:
Refs #94.

What changed:

• Documented that Sketcher internal face generation now handles self-intersecting B-splines and dangling edges.
• Mentioned that split edge fragments keep stable mapped names.
• Kept the update limited to the root Release_notes_1.2 page.

Validation:

• git diff --check -- wiki/Release_notes_1.2.wikitext
• Confirmed the upstream pull/28964 link appears once.
• Confirmed translate tag counts remain balanced.

Notes:

• Translation files were intentionally not modified.
• This is a focused release-note addition and does not claim the broader Sketcher documentation issue is complete.