ATOM-15370 Fix thumbnail scaling and sizing issues

TLDR
Thumbnails size will be removed from the system.
Each thumbnail class is responsible for determining its stored size.
Images and other thumbnail types can be scaled up or down within reason without blurring.

The thumbnail system uses the concept of context and size organize thumbnails by size based on their intended use.  However, most of the thumbnail classes do not respect or use the specified size, which is 16 by 16 pixels and really only usable for small icons.

The thumbnails are currently being used in the asset browser tree control, the larger asset browser previews, the material component property asset controls, the material component inspector for the large preview, and other places.  Each of these places use completely different sizes, some of which are large and change dynamically. Whenever the thumbnails are painted they are scaled to the desired size.

Material and mesh thumbnails were always being captured at 512x512 regardless of what the rest of the thumbnail system said.  Source, product, and folder thumbnails would be stored at the original asset size.  The loading movie thumbnail was always drawn at 16 by 16 and scale up so it was always blurry.  Image thumbnails were always scaled down to 16 by 16 and scale up for larger previews.

Rather than worrying about the size of each context, each thumbnail class will store the image at whenever it deems to be a large enough size that can be scaled down when used.

This may eliminate the need for multiple thumbnail contexts which are not being used anyway.

https://jira.agscollab.com/browse/ATOM-15370

Code/Framework/AzToolsFramework/AzToolsFramework/Thumbnails/LoadingThumbnail.cpp

@@ -18,13 +18,15 @@ namespace AzToolsFramework
 {
     namespace Thumbnailer
     {
+        static constexpr const int LoadingThumbnailSize = 128;
+
         //////////////////////////////////////////////////////////////////////////
         // LoadingThumbnail
         //////////////////////////////////////////////////////////////////////////
         static const char* LoadingIconPath = "Editor/Icons/AssetBrowser/in_progress.gif";
 
-        LoadingThumbnail::LoadingThumbnail(int thumbnailSize)
-            : Thumbnail(MAKE_TKEY(ThumbnailKey), thumbnailSize)
+        LoadingThumbnail::LoadingThumbnail()
+            : Thumbnail(MAKE_TKEY(ThumbnailKey))
             , m_angle(0)
         {
             const char* engineRoot = nullptr;
@@ -34,7 +36,7 @@ namespace AzToolsFramework
             AZ::StringFunc::Path::Join(engineRoot, LoadingIconPath, iconPath);
             m_loadingMovie.setFileName(iconPath.c_str());
             m_loadingMovie.setCacheMode(QMovie::CacheMode::CacheAll);
-            m_loadingMovie.setScaledSize(QSize(m_thumbnailSize, m_thumbnailSize));
+            m_loadingMovie.setScaledSize(QSize(LoadingThumbnailSize, LoadingThumbnailSize));
             m_loadingMovie.start();
             m_pixmap = m_loadingMovie.currentPixmap();
             m_state = State::Ready;