Improve test coverage for Python/C#/TypeScript SDK generators

[ryukzak]

Describe the bug
Right now, we are covered by test only a simple case (core package). We need to test work with multiple packages.

Expected result
In test/api/write-generator path, we will have snapshot tests for more complex scenarios, partly repeated examples/typescript-*:

• sql-on-fhir + tree shake for ViewDefinition
• ccda
• local-package-folder

All scenarios should be fully tested with full toolchain (type checking, building for full generator output) before being fixed as a snapshot. Snapshot should not be full, only most meaningful parts.

Test should be fast enough to be a part of default tests and not require external dependencies (e.g. mypy, etc.).

Additional context
It is not a replacement for examples. It is an additional QA level.