Automatic import of classes/functions/constants on Implement Abstract Functions Quick Fix

Sometimes, especially after #357, there might be new symbol not found errors. These can be solved by the add missing imports quickfix. Parts of that implementation can probably be reused.

Start by reading issue #357 and the existing add missing imports quick fix, since the issue says parts of that implementation can be reused. The work is complete when the Implement Abstract Functions quick fix automatically imports the classes, functions, or constants needed to resolve resulting symbol-not-found errors.

Written by the indexing model from the issue text.