[llvm] [NFC][DebugInfo] Deprecate iterator-taking moveBefore and getFirstNonPHI (PR #124290)

[Orlando Cazalet-Hyams via llvm-commits]

================
@@ -280,14 +280,26 @@ class BasicBlock final : public Value, // Basic blocks are data objects also
   /// When adding instructions to the beginning of the basic block, they should
   /// be added before the returned value, not before the first instruction,
   /// which might be PHI. Returns 0 is there's no non-PHI instruction.
+  ///
+  /// Deprecated in favour of getFirstNonPHIIt, which returns an iterator that
+  /// preserves some debugging information.
+  LLVM_DEPRECATED("Use iterators as instruction positions", "getFirstNonPHIIt")
   const Instruction* getFirstNonPHI() const;
+  LLVM_DEPRECATED("Use iterators as instruction positions", "getFirstNonPHIIt")
----------------
OCHyams wrote:

Thoughts on adding "instead" (or "instead of pointers")- IMO improves clarity as an instruction? YMMV. 

```suggestion
  LLVM_DEPRECATED("Use iterators as instruction positions instead", "getFirstNonPHIIt")
```

https://github.com/llvm/llvm-project/pull/124290