Bug 434446 - [code assist] struct not being recognised as a valid base
class

structs are now being shown as candidates for base classes

while I was at it I also fixed proposals for typedefs, template
parameters and template aliases.

Change-Id: I319b06a195eed88a12969207a21584dc2477219e
Signed-off-by: Michi <woskimi@yahoo.de>
Reviewed-on: https://git.eclipse.org/r/38379
Reviewed-by: Sergey Prigogin <eclipse.sprigogin@gmail.com>
Tested-by: Sergey Prigogin <eclipse.sprigogin@gmail.com>