logic: reduce access to filesystem while indexing

* use canonical filepath cache in cxx indexer
* made constructors of FilePath explicit
* use FilePath at more places instead of string
* forward declares FilePath wherever possible

src/lib/project/Project.cpp

@@ -229,7 +229,7 @@ void Project::load()
 	{
 		m_state = PROJECT_STATE_OUTVERSIONED;
 	}
-	else if (utility::replace(TextAccess::createFromFile(projectSettingsPath.str())->getText(), "\r", "") !=
+	else if (utility::replace(TextAccess::createFromFile(projectSettingsPath)->getText(), "\r", "") !=
 		utility::replace(TextAccess::createFromString(m_storage->getProjectSettingsText())->getText(), "\r", ""))
 	{
 		m_state = PROJECT_STATE_OUTDATED;
@@ -424,7 +424,7 @@ void Project::buildIndex(const std::set<FilePath>& filesToClean, bool fullRefres
 		m_storage->clear();
 	}
 
-	m_storage->setProjectSettingsText(TextAccess::createFromFile(getProjectSettingsFilePath().str())->getText());
+	m_storage->setProjectSettingsText(TextAccess::createFromFile(getProjectSettingsFilePath())->getText());
 
 	std::shared_ptr<TaskGroupSequence> taskSequential = std::make_shared<TaskGroupSequence>();
 

src/lib/project/SourceGroup.cpp

@@ -1,5 +1,7 @@
 #include "project/SourceGroup.h"
 
+#include "utility/file/FilePath.h"
+
 SourceGroup::~SourceGroup()
 {
 }

src/lib/project/SourceGroup.h

@@ -5,10 +5,10 @@
 #include <set>
 #include <vector>
 
-#include "utility/file/FilePath.h"
 #include "settings/LanguageType.h"
 #include "settings/SourceGroupType.h"
 
+class FilePath;
 class IndexerCommand;
 
 class SourceGroup