docs: update PartDesign Body visibility behavior

[Alex-2Code]

Summary

Update the PartDesign Body documentation to reflect the new spacebar visibility behavior introduced in FreeCAD 1.2.

Changes

Updated the Visibility management section of PartDesign_Body.wikitext to document:

• From 3D View: Pressing Space toggles the visibility of the entire Body (not individual features)
• From Tree View: Pressing Space toggles the visibility of the selected object (feature, sketch, datum, etc.)
• Non-geometry features: Sketches, Datums, Binders, etc. always toggle individually regardless of selection source

Context

This change reflects the behavior introduced in:

• FreeCAD PR #29110: Initial change to toggle Body instead of feature from 3D view
• FreeCAD PR #30231: Refined behavior to distinguish between 3D view and tree view selections

Version Note

Added {{Version|1.2}} template to indicate this behavior was introduced in FreeCAD 1.2.

[Reqrefusion]

Do not add T tags yourself; only modify the files in the wiki root directory, do not touch the translation files. Please check the latest version and ensure that the information you are adding has not been added previously. Also, be sure to cite the source of your change. Regression corrections should not be added to the documentation. And it should never contain information that the end user shouldn't know. "It's working as it should" isn't enough to be included. The reasons for each change made, along with their sources, should be explained individually.