Fix implementation chain with internal private classes

[srawlins]

Fixes #2290

Before this fix, RestorableValue lists no implementors. After this fix, RestorableValue lists the following implementors:

RestorableBool, RestorableNum, RestorableString

Fixes #2094

Before this fix, DiagnosticsProperty lists the following implementors:

ColorProperty, DiagnosticsDebugCreator, EnumProperty, ErrorSpacer, FlagProperty, FlagsSummary, IconDataProperty, IterableProperty, MessageProperty, ObjectFlagProperty, ShortcutMapProperty, StringProperty, TransformProperty

After this fix, DiagnosticsProperty lists the following implementors:

ErrorDescription, ErrorHint, ErrorSummary, DoubleProperty, IntProperty, ColorProperty, DiagnosticsDebugCreator, EnumProperty, ErrorSpacer, FlagProperty, FlagsSummary, IconDataProperty, IterableProperty, MessageProperty, ObjectFlagProperty, ShortcutMapProperty, StringProperty, TransformProperty