[llvm] [VPlan] Demarcate VPIs that gen scalars (NFC) (PR #196207)

[Florian Hahn via llvm-commits]

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@@ -1434,12 +1434,12 @@ class LLVM_ABI_FOR_TEST VPInstruction : public VPRecipeWithIRFlags,
 
   /// Returns true if we can generate a scalar for the first lane only if
   /// needed.
-  bool canGenerateScalarForFirstLane() const;
+  bool doesGenerateSingleScalar() const;
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fhahn wrote:

nit: more consistent with other terminology we use elsewhere?
```suggestion
  bool isSingleScalar() const;
```

https://github.com/llvm/llvm-project/pull/196207