Move ImmediateModeShapeDrawer out of Samples

ImmediateModeShapeDrawer is currently located at Shapes/Samples/Assets/Scripts/ImmediateModeShapeDrawer.cs

While it may have originally been created as just an example of how to easily use Immediate Mode drawing on components, the documentation refers to it as 'a helper class you can inherit from' and so at this point it is no longer 'sample' code. It is a core part of the library.

Since it is common practice for users to delete 'Samples' folders from local packages in their projects to save on space and compile time (or even not include the folder in the first place when importing the package from the asset store), I would argue that ImmediateModeShapeDrawer should be moved to a folder outside of 'Samples'.