`ALTER PAGE` cannot set properties on a widget nested inside a `customContent` datagrid column (confirmed on both RnD and Engalar)

[MendixMau]

Environment: mxcli RnD (commit 504aec6) and Engalar (commit 26f2866), Mendix 11.12.0, macOS.

Steps to reproduce:

1. CREATE PAGE with a datagrid containing a column with ShowContentAs: customContent and a
   nested widget (e.g. actionbutton btnEdit) in its body.
2. Attempt ALTER PAGE ... SET Caption = '...' ON <path> targeting btnEdit, trying:
   • 3-level path grid.column.widget
   • 2-level path grid.widget
   • bare widget name

Expected: at least one addressing scheme reaches the nested widget and updates its property.

Actual:

• RnD: 3-level paths are a hard parse error (extraneous input '.' expecting {DROP, ADD, SET, INSERT, REPLACE, '}'}) — the grammar for ON <path> caps at two dotted segments.
  2-level and bare-name paths parse but fail resolution (column "btnEdit" ... not found /
  widget "btnEdit" not found) because the resolver never descends into a customContent
  column's child widgets.
• Engalar: 3-level paths do parse, but are resolved as a layout-grid column reference
  (only DesktopWidth is supported for layout grid column refs) rather than as a path into a
  customContent datagrid column body — so it still never reaches the nested widget. 2-level and
  bare-name paths fail identically to RnD.

Neither build has a working ALTER PAGE path syntax for widgets nested inside customContent
columns, for any property — broader than the already-tracked visible:-on-CONTAINER case. The
workaround for both builds is CREATE OR REPLACE PAGE (full page rewrite) instead of an
in-place ALTER PAGE, when the target is inside a customContent column.