QDoc: Keep authored links to deprecated APIs

Authors can link directly to deprecated APIs. QDoc's TemplateGenerator
drops those references, so readers lose useful navigation. This differs
from the output generated by the HTMLGenerator.

This change aligns the TemplateGenerator with the HTMLGenerator
pipeline. Authored links are now clickable in its output; automatic
links are still suppressed. This preserves the author's intent and keeps
the formats consistent.

Fixes: QTBUG-151277
Pick-to: 6.12
Change-Id: I447efd70a2040a0d5713d48ecb37e9f15bbe4839
Reviewed-by: Topi Reinio <topi.reinio@qt.io>