qdoc: Enable correct linking to externally-built dependencies

So far, there were two types of modular documentation build scenarios
that QDoc supported:

 - All modules are part of the same build, installed to a location with
   known structure. Cross-linking done via relative references:
   <a href="../qtcore/qstring.html">, or

 - All dependencies (.index files) are treated as external documentation
   modules, cross-linking done via full URLs:
   <a href="https://doc.qt.io/qt/qstring.html">.

Enable a mix of these two: that is, a modular build of documentation
(e.g. qt5) with local cross-linking, optionally with addon .index files
pulled into the build. Linking to these external dependencies are done
with full URLs.

QDoc now uses the 'url' configuration variable, recorded in the .index,
to determine whether a dependency is part of the same high-level
project as the one loading the .index file. For example, all
documentation projects in qt5's submodules use a common configuration
that sets a URL, https://doc.qt.io/qt, for all of them.

[ChangeLog][QDoc][QDoc now allows loading external .index files into a
modular documentation build, with correct linking.]

Fixes: QTBUG-107762
Change-Id: Ib6dfb6b76be049f813541be896365b175b224feb
Reviewed-by: Luca Di Sera <luca.disera@qt.io>
(cherry picked from commit e2f237e74dff8b7ee4da03a0adff70d1b8a03e22)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

0 files changed, 0 insertions, 0 deletions