CC-1545: Improve error messages (stderr) for Interpreter scanning error stages

[rohitpaulk]

@andy1li

[andy1li]

@rohitpaulk ready for review.

1. Add [stderr] to indicate which lines are for stderr
2. Add blank lines before and after stderr error messages to make them more readable

---

• lexical_errors/1_missing_line

• lexical_errors/2_mismatch

• lexical_errors/3_extra_line

---

• multiline_errors/1_missing_line

• multiline_errors/2_mismatch

• multiline_errors/3_extra_line

[linear]

CC-1545 Improve error messages (`stderr`) for Interpreter scanning error stages

[rohitpaulk]

Let's try printing out all our assertions for each line in order. Let's make sure to ALWAYS include stdout and stderr, only ignore one of them if there are no lines expected and no lines were printed. In all other cases, we include both.

Stdout lines: 

✅ Line 1
✅ Line 2

Stderr lines: 

— (skipped) Line 1 -- Keep these white
✅ [Line 1] XYZ
- (skipped) Line 2 -- Keep these white
❌ [Line 1] XYZ

Expected: "[Line 2] XYZ"
Received: "[Line 1] XYZ"

Note: 2 lines were skipped since they didn't start with `[Line N]`.