Save a symbol's links from the project database

A symbol's <links_uuids> are now what the project database's link rows
list for it, in their order (projectDataBase::savedLinks()), instead of
a list the save built itself from the symbol's partners: QETZ-DB-FIRST
stage 2a, the save reads links from the database. A symbol the database
does not hold (saved outside a project) still lists them itself.

The rows leave out a partner the project no longer has, so removing a
folio with every folio built no longer saves links to its symbols, as
lazy folios already did (the links part of F113). Every other save is
unchanged.

tst_resaveunchanged removedFolioLeavesNoLinkToIt: affuteuse_250h with
every folio built, folio 3 removed: 4 links named symbols no longer in
the file, none now.

Needs #1522 (each symbol its own uuid) and #1523 (rows in saved order);
local only until both are merged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XCdg2Er2vYhB8Vwa5G7fSR

sources/dataBase/projectdatabase.h

@@ -155,6 +155,7 @@ class projectDataBase : public QObject
 		void conductorUuidChanged(Conductor *conductor, const QUuid &old_uuid);
 		QStringList conductorPropertiesMismatches() const;
 		QStringList linkRowMismatches();
+		bool savedLinks(const Element *element, QList<std::pair<QUuid, int>> *links);
 
 			//Fill the three stores from a project's document before its
 			//folios are built, then, once
@@ -330,6 +331,7 @@ class projectDataBase : public QObject
 			//written: a link is made first and its contact group set after,
 			//so the rows are written when next read, as drawing items are.
 		QList<QPointer<Element>> m_dirty_link_elements;
+		QSqlQuery m_saved_links_query;
 			//Elements moved since their folio cell was last written: a move
 			//sends xChanged and yChanged for every step of a drag, so the
 			//cell is written when next read, as drawing items are.