Turn deprecation message analyze tests back on (#160554)

Additionally:
- Deprecation message analyzer: use AST more instead of regex 
- Deprecation message analyzer: removes some tests since they are in the
formatter's jurisdiction now
- update the analyzer test fixture to fix a couple line numbers
- `@_debugOnly` set `multiline` back to false. The source we get back
from the `ASTNode` doesn't have any line feed characters.

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