Implement code peek feature in the IDE - phase 2

We should implement the code peek feature. For example, by pressing a hotkey, the declaration of the symbol under the cursor is shown in a source code viewer popup. By using this, users do not need to jump to other locations in the source code to quickly check the declaration.

Tasks:

• code peek for included ASN1 file type
  • fixing syntax highlighting of included ASN1 file type (now TTCN-3 syntax highlight is applied instead of ASN1)
• code peek in ASN1 file type