Terminal: rename potential separation to function separation

The checkbox of a terminal element was an all-or-nothing switch: while
it was unticked every conductor property (function, wire colour,
section, number...) crossed to the other side of the terminal, and
once it was ticked nothing did at all.

Rename it to "Function separation" and let one property still cross:
the voltage / protocol, which describes the electrical node itself
rather than one side of it. Conductor::functionSeparatedConductors()
returns the conductors reachable only by crossing such a terminal --
the potential computed with the separations ignored, minus the one
that respects them -- and
ConductorProperties::applyTensionProtocolChange() gives them that one
property, in the conductor properties dialog, the selection panel
multi-edit, the script API and search/replace.

The stored element information stays "potential_isolating", so
existing symbols and projects keep their setting, and the existing
sub-case of terminals sharing a potential-group identifier is
untouched. The German translation of the new label is deliberately
left out of this commit and belongs with the other .ts updates.

sources/qetgraphicsitem/conductor.cpp

@@ -1931,9 +1931,16 @@ void Conductor::displayedTextChanged()
 	@param all_diagram : if true search in all diagram of the project,
 	false search only in the parent diagram of this conductor
 	@param t_list : a list of terminal already found for this potential.
+	@param ignore_function_separation : if true, a terminal element whose
+	function separation is enabled does not stop the search, and the
+	conductors of both its sides are returned as one potential. Only
+	functionSeparatedConductors() passes true.
+	@sa functionSeparatedConductors
 	@return  a QSet of conductor at the same potential.
 */
-QSet<Conductor *> Conductor::relatedPotentialConductors(const bool all_diagram, QList <Terminal *> *t_list)
+QSet<Conductor *> Conductor::relatedPotentialConductors(const bool all_diagram,
+							QList <Terminal *> *t_list,
+							const bool ignore_function_separation)
 {
 	bool declar_t_list = false;
 	if (t_list == nullptr)
@@ -1956,7 +1963,8 @@ QSet<Conductor *> Conductor::relatedPotentialConductors(const bool all_diagram,
 
 				//Get the other terminals of the parent element of @terminal, who share the same potential
 				//This is use for element type "folio report" and "terminal element"
-			for (Terminal *t : relatedPotentialTerminal(terminal, all_diagram))
+			for (Terminal *t : relatedPotentialTerminal(terminal, all_diagram,
+								ignore_function_separation))
 			{
 				if (!t_list->contains(t))
 				{
@@ -1968,7 +1976,8 @@ QSet<Conductor *> Conductor::relatedPotentialConductors(const bool all_diagram,
 			other_conductors_list_t.removeAll(this);
 				//Get the conductors at the same potential for each conductors of other_conductors_list_t
 			for (Conductor *c : other_conductors_list_t) {
-				other_conductors += c->relatedPotentialConductors(all_diagram, t_list);
+				other_conductors += c->relatedPotentialConductors(all_diagram, t_list,
+								  ignore_function_separation);
 			}
 
 			other_conductors += QSet<Conductor*>(other_conductors_list_t.begin(),other_conductors_list_t.end());
@@ -1981,6 +1990,36 @@ QSet<Conductor *> Conductor::relatedPotentialConductors(const bool all_diagram,
 	return(other_conductors);
 }
 
+/**
+	@brief Conductor::functionSeparatedConductors
+	Return the conductors that belong to this conductor's potential only
+	by crossing a function separated terminal element -- a terminal
+	element whose function separation checkbox (element information
+	potential_isolating) is enabled, the checkbox the user ticks to stop
+	sharing a terminal's properties with the other side of the terminal.
+
+	Those conductors are deliberately not part of
+	relatedPotentialConductors(): no property may be copied over them
+	by default. One does cross that separation, though: the voltage /
+	protocol, which describes the electrical node itself. Callers that
+	push it over the whole potential use this method to reach the other
+	side (@see ConductorProperties::applyTensionProtocolChange).
+
+	It is simply the potential computed with the separations ignored,
+	minus the potential that respects them.
+	@param all_diagram : if true search in all diagram of the project,
+	false search only in the parent diagram of this conductor
+	@return a QSet of conductor, this conductor excluded
+*/
+QSet<Conductor *> Conductor::functionSeparatedConductors(const bool all_diagram)
+{
+	QSet<Conductor *> separated = relatedPotentialConductors(all_diagram, nullptr, true);
+	separated.subtract(relatedPotentialConductors(all_diagram));
+	separated.remove(this);
+
+	return separated;
+}
+
 /**
 	@brief Conductor::diagramEditor
 	@return The parent diagram editor or nullptr;