[libcalamares] Tighten up types

- If we're converting a YAML map to a QVariant (Map), may as well
  express that in the types. This makes the return from, say,
  `yamlMapToVariant()` cheaper, but incurs conversion in
  `yamlToVariant()` .. previously the place for costs was
  swapped around.
- For those cases that want-and-expect a Map, or List, this makes
  the calls slightly cheaper. For the generic case, the costs move
  around internally.

src/libcalamares/utils/Yaml.cpp

@@ -89,7 +89,7 @@ yamlScalarToVariant( const YAML::Node& scalarNode )
 }
 
 
-QVariant
+QVariantList
 yamlSequenceToVariant( const YAML::Node& sequenceNode )
 {
     QVariantList vl;
@@ -101,7 +101,7 @@ yamlSequenceToVariant( const YAML::Node& sequenceNode )
 }
 
 
-QVariant
+QVariantMap
 yamlMapToVariant( const YAML::Node& mapNode )
 {
     QVariantMap vm;

src/libcalamares/utils/Yaml.h

@@ -22,6 +22,8 @@
 
 #include <QStringList>
 #include <QVariant>
+#include <QVariantList>
+#include <QVariantMap>
 
 class QByteArray;
 class QFileInfo;
@@ -60,8 +62,8 @@ QVariantMap loadYaml( const QFileInfo&, bool* ok = nullptr );
 
 QVariant yamlToVariant( const YAML::Node& node );
 QVariant yamlScalarToVariant( const YAML::Node& scalarNode );
-QVariant yamlSequenceToVariant( const YAML::Node& sequenceNode );
+QVariantList yamlSequenceToVariant( const YAML::Node& sequenceNode );
-QVariant yamlMapToVariant( const YAML::Node& mapNode );
+QVariantMap yamlMapToVariant( const YAML::Node& mapNode );
 
 /// @brief Returns all the elements of @p listNode in a StringList
 QStringList yamlToStringList( const YAML::Node& listNode );