Core: Apply 'static' pattern to Core::FindPlugin

Also, rename it to Core::Find. It hasn't been a plugin for a while.

Change-Id: I845885ccf18bdc1440258d523b033758d5583881
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/texteditor/findinfiles.cpp

@@ -194,7 +194,7 @@ void FindInFiles::findOnFileSystem(const QString &path)
     const QFileInfo fi(path);
     const QString folder = fi.isDir() ? fi.absoluteFilePath() : fi.absolutePath();
     m_instance->setDirectory(FileName::fromString(folder));
-    FindPlugin::instance()->openFindDialog(m_instance);
+    Find::openFindDialog(m_instance);
 }
 
 FindInFiles *FindInFiles::instance()