Improve content assist - phase 1

Improve content assist processor to provide better/more relevant suggestions

Use cases for proposing:

• module names after "import from"
• module names after "friend module"
• component types where they are relevant, e.g. after "runs on", "system"
• matching/compatible type variables/constants/functions etc. from the visible scope for the right side of an assignment
• matching/compatible type variables/constants/functions etc. from the visible scope for function parameter
• the enumerated items of the matching type for the right side of an assignment
• tags in doc comment section

Generic tasks:

• handle performance issues if a very long list of proposals is generated