[6.0][SourceKit] Allow generation of cursor info for declarations from solutions that haven’t aren’t applied to the AST

[ahoppen]

• Explanation: Previously cursor info for declarations was always extracted from the AST, even if we ran the completion-like fallback cursor info that provides values for ambiguous results in expressions. Change cursor info for declarations in this completion-like path to inspect the constraint system solutions instead. This has two benefits:
  • We can now report ambiguous variable types
  • We are more robust in the generation of results for declarations inside closures. If the closure has an error, we won’t apply the solution to the AST and thus any cursor info that tried to get types out of the AST would fail.
• Scope: Cursor info on declarations if the standard cursor info that inspects the already-built AST fails
• Risk: Low, this fallback only kicks in if the AST-based cursor info fails or produces results with an error type
• Testing: Added a test case
• Issue: rdar://123845208
• Reviewer: @hamishknight on [SourceKit] Allow generation of cursor info for declarations from solutions that haven’t aren’t applied to the AST #72370

[ahoppen]

@swift-ci Please test