Replace hash.keys().contains(k) with hash.contains(k) (35 call sites)

QHash/QMap::keys() allocates a list of every key on each call, then
contains() searches it linearly - an accidental O(n) plus allocation
where a direct O(1) lookup was meant. 35 occurrences across 7 files,
found while profiling project load times (context: #553/#560).

The hot one is ElementPictureFactory::getPictures(), which runs once
per element instance on project load: on the 3399 KiB example project
(191 instances, 129 cache hits) the keys() detour cost 45 ms of the
1.34 s total - measured, not estimated; the fix reproducibly shaves
~35-45 ms off that load. The remaining call sites are UI paths
(search&replace, dynamic text model, undo commands) where the waste
scales with selection/model size.

No behavior change: for QHash/QMap, keys().contains(k) and
contains(k) are equivalent by definition.

(cherry picked from commit 0a7f8f072fa68de7c01a9fc134a4bc8e16d62062)

sources/undocommand/deleteqgraphicsitemcommand.cpp

@@ -86,7 +86,7 @@ DeleteQGraphicsItemCommand::DeleteQGraphicsItemCommand(
 	for (auto table : m_removed_contents.m_tables)
 	{
 			//Table is already managed, jump to next loop
-		if (m_table_scene_hash.keys().contains(table))
+		if (m_table_scene_hash.contains(table))
 			continue;
 
 		auto first_table  = table; //The first table if the table is linked to another
@@ -290,9 +290,9 @@ void DeleteQGraphicsItemCommand::undo()
 
 	for(DynamicElementTextItem *deti : m_removed_contents.m_element_texts)
 	{
-		if(m_elmt_text_hash.keys().contains(deti))
+		if(m_elmt_text_hash.contains(deti))
 			m_elmt_text_hash.value(deti)->addDynamicTextItem(deti);
-		else if (m_grp_texts_hash.keys().contains(deti))
+		else if (m_grp_texts_hash.contains(deti))
 		{
 			Element *elmt = m_grp_texts_hash.value(deti)->parentElement();
 			elmt->addDynamicTextItem(deti);