GUI Basics: Refactor juce_gui_basics file structure

- Created a new detail namespace
- Moved shared module implementation details into the detail namespace
- Split dependencies so source files only rely on details in the detail namespace
- Removed all code from the juce_gui_basics.cpp file

modules/juce_gui_basics/filebrowser/juce_FileBrowserComponent.cpp

@@ -605,7 +605,7 @@ void FileBrowserComponent::getRoots (StringArray& rootNames, StringArray& rootPa
 
 void FileBrowserComponent::timerCallback()
 {
-    const auto isProcessActive = isForegroundOrEmbeddedProcess (this);
+    const auto isProcessActive = detail::WindowingHelpers::isForegroundOrEmbeddedProcess (this);
 
     if (wasProcessActive != isProcessActive)
     {

modules/juce_gui_basics/filebrowser/juce_FileChooser.cpp

@@ -165,7 +165,7 @@ bool FileChooser::browseForDirectory()
 
 bool FileChooser::showDialog (const int flags, FilePreviewComponent* const previewComp)
 {
-    FocusRestorer focusRestorer;
+    detail::FocusRestorer focusRestorer;
 
     pimpl = createPimpl (flags, previewComp);
     pimpl->runModally();

modules/juce_gui_basics/filebrowser/juce_FileChooserDialogBox.cpp

@@ -115,7 +115,7 @@ FileChooserDialogBox::FileChooserDialogBox (const String& name,
     if (parentComp != nullptr)
         parentComp->addAndMakeVisible (this);
     else
-        setAlwaysOnTop (juce_areThereAnyAlwaysOnTopWindows());
+        setAlwaysOnTop (detail::WindowingHelpers::areThereAnyAlwaysOnTopWindows());
 }
 
 FileChooserDialogBox::~FileChooserDialogBox()

modules/juce_gui_basics/filebrowser/juce_FileListComponent.cpp

@@ -26,9 +26,6 @@
 namespace juce
 {
 
-Image juce_createIconForFile (const File& file);
-
-
 //==============================================================================
 FileListComponent::FileListComponent (DirectoryContentsList& listToShow)
     : ListBox ({}, this),
@@ -217,7 +214,7 @@ private:
 
             if (im.isNull() && ! onlyUpdateIfCached)
             {
-                im = juce_createIconForFile (file);
+                im = detail::WindowingHelpers::createIconForFile (file);
 
                 if (im.isValid())
                     ImageCache::addImageToCache (im, hashCode);

modules/juce_gui_basics/filebrowser/juce_FileTreeComponent.cpp

@@ -261,7 +261,7 @@ private:
 
             if (im.isNull() && ! onlyUpdateIfCached)
             {
-                im = juce_createIconForFile (file);
+                im = detail::WindowingHelpers::createIconForFile (file);
 
                 if (im.isValid())
                     ImageCache::addImageToCache (im, hashCode);