[LS] Support more code-suggestions/auto-completions

[SupunS]

Issue To Be Solved

It would be really nice to have code-suggestions and auto-completions for more prominent use cases.

Suggest A Solution

• Can support auto-completions at different levels. e.g: Top-level, statement-level, expression-level, etc.
• Filter the results based on the context. e.g:
  • At the top-level, statements shouldn't be provided as suggestions.
  • Similarly, when the cursor is inside a contract, it should only provide suggestions of the constructs that are allowed within a contract.
• Support completions/suggestions when there are syntax errors.
• May require to introduce resilient parsing to support these.