Doc: Qt Platform Integration: Add missing content to TOC


Add a .qhp subproject for namespaces; QNativeInterface namespace was
missing from TOC.

Likewise, `Mixing Qt with other UI toolkits` was not selected by any of
the .qhp subprojects.

Pick-to: 6.12
Change-Id: I47d6a0fad6f8292aedabb563556ab307da44baa9
Reviewed-by: Alexei Cazacov <alexei.cazacov@qt.io>
commite543058c17e6ce435ad80c671e9af5e2c1dade67
parent7a9f62d878dc90a01bc8b9a053563acf509570ec
authorTopi Reinio <topi.reinio@qt.io>
committerTopi Reinio <topi.reinio@qt.io>
commit timeFri, 23 Oct 2026 07:16:13 +0000