fix: 'explain' omitted the instruction line in some Boolean expressions

[claremacrae]

Description

Fix the explain output for filters inside Boolean expressions, where the filter's explanation was more than a single line.

Previously, the source line was not displayed in that situation, and now it is.

Motivation and Context

Fix #2707

How has this been tested?

• Fix the failing test that I added in 0328f49 to demonstrate this bug.
• Update the results of a few existing tests.
• Exploratory testing.

Screenshots (if appropriate)

Types of changes

Changes visible to users:

• Bug fix (prefix: fix - non-breaking change which fixes an issue)
• Documentation (prefix: docs - improvements to any documentation content for users)

Internal changes:

• Refactor (prefix: refactor - non-breaking change which only improves the design or structure of existing code, and making no changes to its external behaviour)
• Tests (prefix: test - additions and improvements to unit tests and the smoke tests)

Checklist

• My code follows the code style of this project and passes yarn run lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• My change has adequate Unit Test coverage.

Terms

• My contribution follow this project's contributing guide
• I agree to follow this project's Code of Conduct