Function. This is step 18/n towards merging instructions and statements, NFC. PiperOrigin-RevId: 227139399
StmtSuccessorIterator/StmtSuccessorIterator, and rename and move the CFGFunctionViewGraph pass to ViewFunctionGraph. This is step 13/n towards merging instructions and statements, NFC. PiperOrigin-RevId: 227069438