fix: split if-return chains in string-dispatch and type-system

[cs01]

Summary

• Split dispatchStringMethod() (20+ consecutive if-returns) into 4 helper functions with ≤4 branches each
• Split dispatchArrayMethod() (12+ consecutive if-returns) into 4 helper functions with ≤4 branches each
• Split canonicalTypeToLlvm() (11+ consecutive if-returns) into 5 helper functions with ≤4 branches each

Mitigates the native compiler's if-drop bug (5th+ consecutive if-return blocks get silently dropped in Stage 0).

Test plan

• npx tsc --noEmit passes
• all 434 tests pass
• npm run verify:quick passes (self-hosting Stage 0 + Stage 1)

[cs01]

Shouldn't we fix the root cause of the if drop on 5th if return block? Fix it or at the very least throw a fatal error from the compiler